diff --git a/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/ClientUtils.mustache b/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/ClientUtils.mustache
index 9eea09d438e7..ae83297b1d50 100644
--- a/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/ClientUtils.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/ClientUtils.mustache
@@ -158,7 +158,7 @@ using System.Runtime.CompilerServices;
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string{{nrt?}} ParameterToString(object obj, string{{nrt?}} format = ISO8601_DATETIME_FORMAT)
+        public static string{{nrt?}} ParameterToString(object{{nrt?}} obj, string{{nrt?}} format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/api.mustache b/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/api.mustache
index cdb97b18b821..ac482b8d2742 100644
--- a/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/api.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/api.mustache
@@ -423,9 +423,7 @@ namespace {{packageName}}.{{apiPackage}}
                     {{#-first}}
 
                     {{/-first}}
-                    {{/required}}
-                    {{#required}}
-                    parseQueryStringLocalVar["{{baseName}}"] = {{paramName}}{{#isNullable}}{{nrt?}}{{^nrt}}{{#vendorExtensions.x-is-value-type}}?{{/vendorExtensions.x-is-value-type}}{{/nrt}}{{/isNullable}}.ToString();
+                    parseQueryStringLocalVar["{{baseName}}"] = ClientUtils.ParameterToString({{paramName}});
                     {{/required}}
                     {{/queryParams}}
 
@@ -438,7 +436,8 @@ namespace {{packageName}}.{{apiPackage}}
                     {{#queryParams}}
                     {{^required}}
                     if ({{paramName}}.IsSet)
-                        parseQueryStringLocalVar["{{baseName}}"] = {{paramName}}.Value{{#isNullable}}{{nrt?}}{{^nrt}}{{#vendorExtensions.x-is-value-type}}?{{/vendorExtensions.x-is-value-type}}{{/nrt}}{{/isNullable}}.ToString();
+                        // here too
+                        parseQueryStringLocalVar["{{baseName}}"] = ClientUtils.ParameterToString({{paramName}}.Value);
 
                     {{/required}}
                     {{#-last}}
diff --git a/samples/client/petstore/csharp/generichost/net8/AllOf/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/AllOf/src/Org.OpenAPITools/Client/ClientUtils.cs
index 80fd40849a10..76ccb5126adf 100644
--- a/samples/client/petstore/csharp/generichost/net8/AllOf/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/AllOf/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -117,7 +117,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/AnyOf/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/AnyOf/src/Org.OpenAPITools/Client/ClientUtils.cs
index 43fc1f290728..57169a68de3b 100644
--- a/samples/client/petstore/csharp/generichost/net8/AnyOf/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/AnyOf/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -117,7 +117,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/AnyOfNoCompare/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/AnyOfNoCompare/src/Org.OpenAPITools/Client/ClientUtils.cs
index 6742fbaabdde..fcb4e3b1152b 100644
--- a/samples/client/petstore/csharp/generichost/net8/AnyOfNoCompare/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/AnyOfNoCompare/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -102,7 +102,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/FakeApi.cs
index faca97872b06..218bb51d7b46 100644
--- a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2155,7 +2155,7 @@ public async Task<IFakeOuterStringSerializeApiResponse> FakeOuterStringSerialize
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_uuid"] = requiredStringUuid.ToString();
+                    parseQueryStringLocalVar["required_string_uuid"] = ClientUtils.ParameterToString(requiredStringUuid);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -2974,7 +2974,7 @@ public async Task<ITestBodyWithQueryParamsApiResponse> TestBodyWithQueryParamsAs
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["query"] = query.ToString();
+                    parseQueryStringLocalVar["query"] = ClientUtils.ParameterToString(query);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -3796,16 +3796,20 @@ public async Task<ITestEnumParametersApiResponse> TestEnumParametersAsync(Option
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
                     if (enumQueryStringArray.IsSet)
-                        parseQueryStringLocalVar["enum_query_string_array"] = enumQueryStringArray.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string_array"] = ClientUtils.ParameterToString(enumQueryStringArray.Value);
 
                     if (enumQueryString.IsSet)
-                        parseQueryStringLocalVar["enum_query_string"] = enumQueryString.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string"] = ClientUtils.ParameterToString(enumQueryString.Value);
 
                     if (enumQueryDouble.IsSet)
-                        parseQueryStringLocalVar["enum_query_double"] = enumQueryDouble.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_double"] = ClientUtils.ParameterToString(enumQueryDouble.Value);
 
                     if (enumQueryInteger.IsSet)
-                        parseQueryStringLocalVar["enum_query_integer"] = enumQueryInteger.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_integer"] = ClientUtils.ParameterToString(enumQueryInteger.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4037,14 +4041,16 @@ public async Task<ITestGroupParametersApiResponse> TestGroupParametersAsync(bool
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_group"] = requiredStringGroup.ToString();
-                    parseQueryStringLocalVar["required_int64_group"] = requiredInt64Group.ToString();
+                    parseQueryStringLocalVar["required_string_group"] = ClientUtils.ParameterToString(requiredStringGroup);
+                    parseQueryStringLocalVar["required_int64_group"] = ClientUtils.ParameterToString(requiredInt64Group);
 
                     if (stringGroup.IsSet)
-                        parseQueryStringLocalVar["string_group"] = stringGroup.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["string_group"] = ClientUtils.ParameterToString(stringGroup.Value);
 
                     if (int64Group.IsSet)
-                        parseQueryStringLocalVar["int64_group"] = int64Group.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["int64_group"] = ClientUtils.ParameterToString(int64Group.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4899,19 +4905,21 @@ public async Task<ITestQueryParameterCollectionFormatApiResponse> TestQueryParam
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["pipe"] = pipe.ToString();
-                    parseQueryStringLocalVar["ioutil"] = ioutil.ToString();
-                    parseQueryStringLocalVar["http"] = http.ToString();
-                    parseQueryStringLocalVar["url"] = url.ToString();
-                    parseQueryStringLocalVar["context"] = context.ToString();
-                    parseQueryStringLocalVar["requiredNotNullable"] = requiredNotNullable.ToString();
-                    parseQueryStringLocalVar["requiredNullable"] = requiredNullable.ToString();
+                    parseQueryStringLocalVar["pipe"] = ClientUtils.ParameterToString(pipe);
+                    parseQueryStringLocalVar["ioutil"] = ClientUtils.ParameterToString(ioutil);
+                    parseQueryStringLocalVar["http"] = ClientUtils.ParameterToString(http);
+                    parseQueryStringLocalVar["url"] = ClientUtils.ParameterToString(url);
+                    parseQueryStringLocalVar["context"] = ClientUtils.ParameterToString(context);
+                    parseQueryStringLocalVar["requiredNotNullable"] = ClientUtils.ParameterToString(requiredNotNullable);
+                    parseQueryStringLocalVar["requiredNullable"] = ClientUtils.ParameterToString(requiredNullable);
 
                     if (notRequiredNotNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNotNullable"] = notRequiredNotNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNotNullable"] = ClientUtils.ParameterToString(notRequiredNotNullable.Value);
 
                     if (notRequiredNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNullable"] = notRequiredNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNullable"] = ClientUtils.ParameterToString(notRequiredNullable.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/PetApi.cs b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/PetApi.cs
index b94ad700fe85..c75d22024d39 100644
--- a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/PetApi.cs
@@ -1173,7 +1173,7 @@ public async Task<IFindPetsByStatusApiResponse> FindPetsByStatusAsync(List<FindP
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["status"] = status.ToString();
+                    parseQueryStringLocalVar["status"] = ClientUtils.ParameterToString(status);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -1424,7 +1424,7 @@ public async Task<IFindPetsByTagsApiResponse> FindPetsByTagsAsync(List<string> t
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["tags"] = tags.ToString();
+                    parseQueryStringLocalVar["tags"] = ClientUtils.ParameterToString(tags);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/UserApi.cs b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/UserApi.cs
index b41d2d18c987..a6543a9dc4a8 100644
--- a/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/FormModels/src/Org.OpenAPITools/Api/UserApi.cs
@@ -1745,8 +1745,8 @@ public async Task<ILoginUserApiResponse> LoginUserAsync(string username, string
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["username"] = username.ToString();
-                    parseQueryStringLocalVar["password"] = password.ToString();
+                    parseQueryStringLocalVar["username"] = ClientUtils.ParameterToString(username);
+                    parseQueryStringLocalVar["password"] = ClientUtils.ParameterToString(password);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/FakeApi.cs
index d7f32767b505..2bb291f16f5e 100644
--- a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2157,7 +2157,7 @@ public async Task<IFakeOuterStringSerializeApiResponse> FakeOuterStringSerialize
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_uuid"] = requiredStringUuid.ToString();
+                    parseQueryStringLocalVar["required_string_uuid"] = ClientUtils.ParameterToString(requiredStringUuid);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -2976,7 +2976,7 @@ public async Task<ITestBodyWithQueryParamsApiResponse> TestBodyWithQueryParamsAs
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["query"] = query.ToString();
+                    parseQueryStringLocalVar["query"] = ClientUtils.ParameterToString(query);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -3810,16 +3810,20 @@ public async Task<ITestEnumParametersApiResponse> TestEnumParametersAsync(Option
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
                     if (enumQueryStringArray.IsSet)
-                        parseQueryStringLocalVar["enum_query_string_array"] = enumQueryStringArray.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string_array"] = ClientUtils.ParameterToString(enumQueryStringArray.Value);
 
                     if (enumQueryDouble.IsSet)
-                        parseQueryStringLocalVar["enum_query_double"] = enumQueryDouble.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_double"] = ClientUtils.ParameterToString(enumQueryDouble.Value);
 
                     if (enumQueryInteger.IsSet)
-                        parseQueryStringLocalVar["enum_query_integer"] = enumQueryInteger.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_integer"] = ClientUtils.ParameterToString(enumQueryInteger.Value);
 
                     if (enumQueryString.IsSet)
-                        parseQueryStringLocalVar["enum_query_string"] = enumQueryString.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string"] = ClientUtils.ParameterToString(enumQueryString.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4051,14 +4055,16 @@ public async Task<ITestGroupParametersApiResponse> TestGroupParametersAsync(bool
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_group"] = requiredStringGroup.ToString();
-                    parseQueryStringLocalVar["required_int64_group"] = requiredInt64Group.ToString();
+                    parseQueryStringLocalVar["required_string_group"] = ClientUtils.ParameterToString(requiredStringGroup);
+                    parseQueryStringLocalVar["required_int64_group"] = ClientUtils.ParameterToString(requiredInt64Group);
 
                     if (stringGroup.IsSet)
-                        parseQueryStringLocalVar["string_group"] = stringGroup.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["string_group"] = ClientUtils.ParameterToString(stringGroup.Value);
 
                     if (int64Group.IsSet)
-                        parseQueryStringLocalVar["int64_group"] = int64Group.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["int64_group"] = ClientUtils.ParameterToString(int64Group.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4913,19 +4919,21 @@ public async Task<ITestQueryParameterCollectionFormatApiResponse> TestQueryParam
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["pipe"] = pipe.ToString();
-                    parseQueryStringLocalVar["ioutil"] = ioutil.ToString();
-                    parseQueryStringLocalVar["http"] = http.ToString();
-                    parseQueryStringLocalVar["url"] = url.ToString();
-                    parseQueryStringLocalVar["context"] = context.ToString();
-                    parseQueryStringLocalVar["requiredNotNullable"] = requiredNotNullable.ToString();
-                    parseQueryStringLocalVar["requiredNullable"] = requiredNullable?.ToString();
+                    parseQueryStringLocalVar["pipe"] = ClientUtils.ParameterToString(pipe);
+                    parseQueryStringLocalVar["ioutil"] = ClientUtils.ParameterToString(ioutil);
+                    parseQueryStringLocalVar["http"] = ClientUtils.ParameterToString(http);
+                    parseQueryStringLocalVar["url"] = ClientUtils.ParameterToString(url);
+                    parseQueryStringLocalVar["context"] = ClientUtils.ParameterToString(context);
+                    parseQueryStringLocalVar["requiredNotNullable"] = ClientUtils.ParameterToString(requiredNotNullable);
+                    parseQueryStringLocalVar["requiredNullable"] = ClientUtils.ParameterToString(requiredNullable);
 
                     if (notRequiredNotNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNotNullable"] = notRequiredNotNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNotNullable"] = ClientUtils.ParameterToString(notRequiredNotNullable.Value);
 
                     if (notRequiredNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNullable"] = notRequiredNullable.Value?.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNullable"] = ClientUtils.ParameterToString(notRequiredNullable.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/PetApi.cs b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/PetApi.cs
index b302ea0482b1..21ed363826b2 100644
--- a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/PetApi.cs
@@ -1175,7 +1175,7 @@ public async Task<IFindPetsByStatusApiResponse> FindPetsByStatusAsync(List<strin
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["status"] = status.ToString();
+                    parseQueryStringLocalVar["status"] = ClientUtils.ParameterToString(status);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -1426,7 +1426,7 @@ public async Task<IFindPetsByTagsApiResponse> FindPetsByTagsAsync(List<string> t
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["tags"] = tags.ToString();
+                    parseQueryStringLocalVar["tags"] = ClientUtils.ParameterToString(tags);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/UserApi.cs b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/UserApi.cs
index ebe235bc9d7d..8752acf36790 100644
--- a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Api/UserApi.cs
@@ -1747,8 +1747,8 @@ public async Task<ILoginUserApiResponse> LoginUserAsync(string username, string
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["username"] = username.ToString();
-                    parseQueryStringLocalVar["password"] = password.ToString();
+                    parseQueryStringLocalVar["username"] = ClientUtils.ParameterToString(username);
+                    parseQueryStringLocalVar["password"] = ClientUtils.ParameterToString(password);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Client/ClientUtils.cs
index caafbfef6e56..7c68fd649ffd 100644
--- a/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/NullReferenceTypes/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -148,7 +148,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools/Client/ClientUtils.cs
index 43fc1f290728..57169a68de3b 100644
--- a/samples/client/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -117,7 +117,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
index 4e476c366977..987454df7ee3 100644
--- a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2155,7 +2155,7 @@ public async Task<IFakeOuterStringSerializeApiResponse> FakeOuterStringSerialize
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_uuid"] = requiredStringUuid.ToString();
+                    parseQueryStringLocalVar["required_string_uuid"] = ClientUtils.ParameterToString(requiredStringUuid);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -2974,7 +2974,7 @@ public async Task<ITestBodyWithQueryParamsApiResponse> TestBodyWithQueryParamsAs
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["query"] = query.ToString();
+                    parseQueryStringLocalVar["query"] = ClientUtils.ParameterToString(query);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -3808,16 +3808,20 @@ public async Task<ITestEnumParametersApiResponse> TestEnumParametersAsync(Option
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
                     if (enumQueryStringArray.IsSet)
-                        parseQueryStringLocalVar["enum_query_string_array"] = enumQueryStringArray.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string_array"] = ClientUtils.ParameterToString(enumQueryStringArray.Value);
 
                     if (enumQueryDouble.IsSet)
-                        parseQueryStringLocalVar["enum_query_double"] = enumQueryDouble.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_double"] = ClientUtils.ParameterToString(enumQueryDouble.Value);
 
                     if (enumQueryInteger.IsSet)
-                        parseQueryStringLocalVar["enum_query_integer"] = enumQueryInteger.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_integer"] = ClientUtils.ParameterToString(enumQueryInteger.Value);
 
                     if (enumQueryString.IsSet)
-                        parseQueryStringLocalVar["enum_query_string"] = enumQueryString.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string"] = ClientUtils.ParameterToString(enumQueryString.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4049,14 +4053,16 @@ public async Task<ITestGroupParametersApiResponse> TestGroupParametersAsync(bool
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_group"] = requiredStringGroup.ToString();
-                    parseQueryStringLocalVar["required_int64_group"] = requiredInt64Group.ToString();
+                    parseQueryStringLocalVar["required_string_group"] = ClientUtils.ParameterToString(requiredStringGroup);
+                    parseQueryStringLocalVar["required_int64_group"] = ClientUtils.ParameterToString(requiredInt64Group);
 
                     if (stringGroup.IsSet)
-                        parseQueryStringLocalVar["string_group"] = stringGroup.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["string_group"] = ClientUtils.ParameterToString(stringGroup.Value);
 
                     if (int64Group.IsSet)
-                        parseQueryStringLocalVar["int64_group"] = int64Group.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["int64_group"] = ClientUtils.ParameterToString(int64Group.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4911,19 +4917,21 @@ public async Task<ITestQueryParameterCollectionFormatApiResponse> TestQueryParam
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["pipe"] = pipe.ToString();
-                    parseQueryStringLocalVar["ioutil"] = ioutil.ToString();
-                    parseQueryStringLocalVar["http"] = http.ToString();
-                    parseQueryStringLocalVar["url"] = url.ToString();
-                    parseQueryStringLocalVar["context"] = context.ToString();
-                    parseQueryStringLocalVar["requiredNotNullable"] = requiredNotNullable.ToString();
-                    parseQueryStringLocalVar["requiredNullable"] = requiredNullable.ToString();
+                    parseQueryStringLocalVar["pipe"] = ClientUtils.ParameterToString(pipe);
+                    parseQueryStringLocalVar["ioutil"] = ClientUtils.ParameterToString(ioutil);
+                    parseQueryStringLocalVar["http"] = ClientUtils.ParameterToString(http);
+                    parseQueryStringLocalVar["url"] = ClientUtils.ParameterToString(url);
+                    parseQueryStringLocalVar["context"] = ClientUtils.ParameterToString(context);
+                    parseQueryStringLocalVar["requiredNotNullable"] = ClientUtils.ParameterToString(requiredNotNullable);
+                    parseQueryStringLocalVar["requiredNullable"] = ClientUtils.ParameterToString(requiredNullable);
 
                     if (notRequiredNotNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNotNullable"] = notRequiredNotNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNotNullable"] = ClientUtils.ParameterToString(notRequiredNotNullable.Value);
 
                     if (notRequiredNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNullable"] = notRequiredNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNullable"] = ClientUtils.ParameterToString(notRequiredNullable.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/PetApi.cs b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
index 9284aeb1b9cd..1b402e88658c 100644
--- a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
@@ -1173,7 +1173,7 @@ public async Task<IFindPetsByStatusApiResponse> FindPetsByStatusAsync(List<strin
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["status"] = status.ToString();
+                    parseQueryStringLocalVar["status"] = ClientUtils.ParameterToString(status);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -1424,7 +1424,7 @@ public async Task<IFindPetsByTagsApiResponse> FindPetsByTagsAsync(List<string> t
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["tags"] = tags.ToString();
+                    parseQueryStringLocalVar["tags"] = ClientUtils.ParameterToString(tags);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/UserApi.cs b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
index b41d2d18c987..a6543a9dc4a8 100644
--- a/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
@@ -1745,8 +1745,8 @@ public async Task<ILoginUserApiResponse> LoginUserAsync(string username, string
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["username"] = username.ToString();
-                    parseQueryStringLocalVar["password"] = password.ToString();
+                    parseQueryStringLocalVar["username"] = ClientUtils.ParameterToString(username);
+                    parseQueryStringLocalVar["password"] = ClientUtils.ParameterToString(password);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/FakeApi.cs
index d7f32767b505..2bb291f16f5e 100644
--- a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2157,7 +2157,7 @@ public async Task<IFakeOuterStringSerializeApiResponse> FakeOuterStringSerialize
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_uuid"] = requiredStringUuid.ToString();
+                    parseQueryStringLocalVar["required_string_uuid"] = ClientUtils.ParameterToString(requiredStringUuid);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -2976,7 +2976,7 @@ public async Task<ITestBodyWithQueryParamsApiResponse> TestBodyWithQueryParamsAs
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["query"] = query.ToString();
+                    parseQueryStringLocalVar["query"] = ClientUtils.ParameterToString(query);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -3810,16 +3810,20 @@ public async Task<ITestEnumParametersApiResponse> TestEnumParametersAsync(Option
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
                     if (enumQueryStringArray.IsSet)
-                        parseQueryStringLocalVar["enum_query_string_array"] = enumQueryStringArray.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string_array"] = ClientUtils.ParameterToString(enumQueryStringArray.Value);
 
                     if (enumQueryDouble.IsSet)
-                        parseQueryStringLocalVar["enum_query_double"] = enumQueryDouble.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_double"] = ClientUtils.ParameterToString(enumQueryDouble.Value);
 
                     if (enumQueryInteger.IsSet)
-                        parseQueryStringLocalVar["enum_query_integer"] = enumQueryInteger.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_integer"] = ClientUtils.ParameterToString(enumQueryInteger.Value);
 
                     if (enumQueryString.IsSet)
-                        parseQueryStringLocalVar["enum_query_string"] = enumQueryString.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string"] = ClientUtils.ParameterToString(enumQueryString.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4051,14 +4055,16 @@ public async Task<ITestGroupParametersApiResponse> TestGroupParametersAsync(bool
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_group"] = requiredStringGroup.ToString();
-                    parseQueryStringLocalVar["required_int64_group"] = requiredInt64Group.ToString();
+                    parseQueryStringLocalVar["required_string_group"] = ClientUtils.ParameterToString(requiredStringGroup);
+                    parseQueryStringLocalVar["required_int64_group"] = ClientUtils.ParameterToString(requiredInt64Group);
 
                     if (stringGroup.IsSet)
-                        parseQueryStringLocalVar["string_group"] = stringGroup.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["string_group"] = ClientUtils.ParameterToString(stringGroup.Value);
 
                     if (int64Group.IsSet)
-                        parseQueryStringLocalVar["int64_group"] = int64Group.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["int64_group"] = ClientUtils.ParameterToString(int64Group.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4913,19 +4919,21 @@ public async Task<ITestQueryParameterCollectionFormatApiResponse> TestQueryParam
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["pipe"] = pipe.ToString();
-                    parseQueryStringLocalVar["ioutil"] = ioutil.ToString();
-                    parseQueryStringLocalVar["http"] = http.ToString();
-                    parseQueryStringLocalVar["url"] = url.ToString();
-                    parseQueryStringLocalVar["context"] = context.ToString();
-                    parseQueryStringLocalVar["requiredNotNullable"] = requiredNotNullable.ToString();
-                    parseQueryStringLocalVar["requiredNullable"] = requiredNullable?.ToString();
+                    parseQueryStringLocalVar["pipe"] = ClientUtils.ParameterToString(pipe);
+                    parseQueryStringLocalVar["ioutil"] = ClientUtils.ParameterToString(ioutil);
+                    parseQueryStringLocalVar["http"] = ClientUtils.ParameterToString(http);
+                    parseQueryStringLocalVar["url"] = ClientUtils.ParameterToString(url);
+                    parseQueryStringLocalVar["context"] = ClientUtils.ParameterToString(context);
+                    parseQueryStringLocalVar["requiredNotNullable"] = ClientUtils.ParameterToString(requiredNotNullable);
+                    parseQueryStringLocalVar["requiredNullable"] = ClientUtils.ParameterToString(requiredNullable);
 
                     if (notRequiredNotNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNotNullable"] = notRequiredNotNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNotNullable"] = ClientUtils.ParameterToString(notRequiredNotNullable.Value);
 
                     if (notRequiredNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNullable"] = notRequiredNullable.Value?.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNullable"] = ClientUtils.ParameterToString(notRequiredNullable.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/PetApi.cs b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/PetApi.cs
index b302ea0482b1..21ed363826b2 100644
--- a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/PetApi.cs
@@ -1175,7 +1175,7 @@ public async Task<IFindPetsByStatusApiResponse> FindPetsByStatusAsync(List<strin
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["status"] = status.ToString();
+                    parseQueryStringLocalVar["status"] = ClientUtils.ParameterToString(status);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -1426,7 +1426,7 @@ public async Task<IFindPetsByTagsApiResponse> FindPetsByTagsAsync(List<string> t
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["tags"] = tags.ToString();
+                    parseQueryStringLocalVar["tags"] = ClientUtils.ParameterToString(tags);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/UserApi.cs b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/UserApi.cs
index ebe235bc9d7d..8752acf36790 100644
--- a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Api/UserApi.cs
@@ -1747,8 +1747,8 @@ public async Task<ILoginUserApiResponse> LoginUserAsync(string username, string
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["username"] = username.ToString();
-                    parseQueryStringLocalVar["password"] = password.ToString();
+                    parseQueryStringLocalVar["username"] = ClientUtils.ParameterToString(username);
+                    parseQueryStringLocalVar["password"] = ClientUtils.ParameterToString(password);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Client/ClientUtils.cs
index caafbfef6e56..7c68fd649ffd 100644
--- a/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/SourceGeneration/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -148,7 +148,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp/generichost/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/ClientUtils.cs
index 03822d5f806d..713da49169c4 100644
--- a/samples/client/petstore/csharp/generichost/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp/generichost/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -102,7 +102,7 @@ public static string SanitizeFilename(string filename)
         /// <param name="obj">The parameter (header, path, query, form).</param>
         /// <param name="format">The DateTime serialization format.</param>
         /// <returns>Formatted string.</returns>
-        public static string? ParameterToString(object obj, string? format = ISO8601_DATETIME_FORMAT)
+        public static string? ParameterToString(object? obj, string? format = ISO8601_DATETIME_FORMAT)
         {
             if (obj is DateTime dateTime)
                 // Return a formatted date string - Can be customized with Configuration.DateTimeFormat
diff --git a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
index ee74e8e0603f..ad69a02434e6 100644
--- a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2150,7 +2150,7 @@ public async Task<IFakeOuterStringSerializeApiResponse> FakeOuterStringSerialize
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_uuid"] = requiredStringUuid.ToString();
+                    parseQueryStringLocalVar["required_string_uuid"] = ClientUtils.ParameterToString(requiredStringUuid);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -2967,7 +2967,7 @@ public async Task<ITestBodyWithQueryParamsApiResponse> TestBodyWithQueryParamsAs
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["query"] = query.ToString();
+                    parseQueryStringLocalVar["query"] = ClientUtils.ParameterToString(query);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -3800,16 +3800,20 @@ public async Task<ITestEnumParametersApiResponse> TestEnumParametersAsync(Option
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
                     if (enumQueryStringArray.IsSet)
-                        parseQueryStringLocalVar["enum_query_string_array"] = enumQueryStringArray.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string_array"] = ClientUtils.ParameterToString(enumQueryStringArray.Value);
 
                     if (enumQueryDouble.IsSet)
-                        parseQueryStringLocalVar["enum_query_double"] = enumQueryDouble.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_double"] = ClientUtils.ParameterToString(enumQueryDouble.Value);
 
                     if (enumQueryInteger.IsSet)
-                        parseQueryStringLocalVar["enum_query_integer"] = enumQueryInteger.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_integer"] = ClientUtils.ParameterToString(enumQueryInteger.Value);
 
                     if (enumQueryString.IsSet)
-                        parseQueryStringLocalVar["enum_query_string"] = enumQueryString.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["enum_query_string"] = ClientUtils.ParameterToString(enumQueryString.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4041,14 +4045,16 @@ public async Task<ITestGroupParametersApiResponse> TestGroupParametersAsync(bool
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["required_string_group"] = requiredStringGroup.ToString();
-                    parseQueryStringLocalVar["required_int64_group"] = requiredInt64Group.ToString();
+                    parseQueryStringLocalVar["required_string_group"] = ClientUtils.ParameterToString(requiredStringGroup);
+                    parseQueryStringLocalVar["required_int64_group"] = ClientUtils.ParameterToString(requiredInt64Group);
 
                     if (stringGroup.IsSet)
-                        parseQueryStringLocalVar["string_group"] = stringGroup.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["string_group"] = ClientUtils.ParameterToString(stringGroup.Value);
 
                     if (int64Group.IsSet)
-                        parseQueryStringLocalVar["int64_group"] = int64Group.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["int64_group"] = ClientUtils.ParameterToString(int64Group.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -4902,19 +4908,21 @@ public async Task<ITestQueryParameterCollectionFormatApiResponse> TestQueryParam
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["pipe"] = pipe.ToString();
-                    parseQueryStringLocalVar["ioutil"] = ioutil.ToString();
-                    parseQueryStringLocalVar["http"] = http.ToString();
-                    parseQueryStringLocalVar["url"] = url.ToString();
-                    parseQueryStringLocalVar["context"] = context.ToString();
-                    parseQueryStringLocalVar["requiredNotNullable"] = requiredNotNullable.ToString();
-                    parseQueryStringLocalVar["requiredNullable"] = requiredNullable.ToString();
+                    parseQueryStringLocalVar["pipe"] = ClientUtils.ParameterToString(pipe);
+                    parseQueryStringLocalVar["ioutil"] = ClientUtils.ParameterToString(ioutil);
+                    parseQueryStringLocalVar["http"] = ClientUtils.ParameterToString(http);
+                    parseQueryStringLocalVar["url"] = ClientUtils.ParameterToString(url);
+                    parseQueryStringLocalVar["context"] = ClientUtils.ParameterToString(context);
+                    parseQueryStringLocalVar["requiredNotNullable"] = ClientUtils.ParameterToString(requiredNotNullable);
+                    parseQueryStringLocalVar["requiredNullable"] = ClientUtils.ParameterToString(requiredNullable);
 
                     if (notRequiredNotNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNotNullable"] = notRequiredNotNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNotNullable"] = ClientUtils.ParameterToString(notRequiredNotNullable.Value);
 
                     if (notRequiredNullable.IsSet)
-                        parseQueryStringLocalVar["notRequiredNullable"] = notRequiredNullable.Value.ToString();
+                        // here too
+                        parseQueryStringLocalVar["notRequiredNullable"] = ClientUtils.ParameterToString(notRequiredNullable.Value);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/PetApi.cs b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
index 89f7ca4a919e..88051a3d0053 100644
--- a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/PetApi.cs
@@ -1171,7 +1171,7 @@ public async Task<IFindPetsByStatusApiResponse> FindPetsByStatusAsync(List<strin
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["status"] = status.ToString();
+                    parseQueryStringLocalVar["status"] = ClientUtils.ParameterToString(status);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
@@ -1421,7 +1421,7 @@ public async Task<IFindPetsByTagsApiResponse> FindPetsByTagsAsync(List<string> t
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["tags"] = tags.ToString();
+                    parseQueryStringLocalVar["tags"] = ClientUtils.ParameterToString(tags);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();
 
diff --git a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/UserApi.cs b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
index 9d668e774136..375b1aa874e8 100644
--- a/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/generichost/standard2.0/Petstore/src/Org.OpenAPITools/Api/UserApi.cs
@@ -1734,8 +1734,8 @@ public async Task<ILoginUserApiResponse> LoginUserAsync(string username, string
 
                     System.Collections.Specialized.NameValueCollection parseQueryStringLocalVar = System.Web.HttpUtility.ParseQueryString(string.Empty);
 
-                    parseQueryStringLocalVar["username"] = username.ToString();
-                    parseQueryStringLocalVar["password"] = password.ToString();
+                    parseQueryStringLocalVar["username"] = ClientUtils.ParameterToString(username);
+                    parseQueryStringLocalVar["password"] = ClientUtils.ParameterToString(password);
 
                     uriBuilderLocalVar.Query = parseQueryStringLocalVar.ToString();