chore!: Enable nullable reference types (#253)

<!-- Please use this template for your pull request. -->
<!-- Please use the sections that you need and delete other sections -->

## Enable nullable reference types
<!-- add the description of the PR here -->

- This PR enables the nullable validation and treats warnings as errors.

### Related Issues
<!-- add here the GitHub issue that this PR resolves if applicable -->

Fixes #208 

### Notes
<!-- any additional notes for this PR -->
This PR turns on the nullable checks for the dotnet checks. This gives
us a better and safer codebase since it checks for potential null
exceptions.

### Breaking changes
While this PR won't require changes to the exposed API, it might show
some errors to the clients consuming it.

---------

Signed-off-by: André Silva <[email protected]>

Author: askpt

build/Common.props

@@ -6,6 +6,8 @@
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
     <!-- Workaround for IDE0005 (Remove unnecessary usings/imports); see https://github.com/dotnet/roslyn/issues/41640 -->
     <NoWarn>EnableGenerateDocumentationFile</NoWarn>
+    <Nullable>enable</Nullable>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)'=='Debug'">

src/OpenFeature/Api.cs

@@ -54,7 +54,7 @@ public void SetProvider(FeatureProvider featureProvider)
         /// </summary>
         /// <remarks>The provider cannot be set to null. Attempting to set the provider to null has no effect.</remarks>
         /// <param name="featureProvider">Implementation of <see cref="FeatureProvider"/></param>
-        public async Task SetProviderAsync(FeatureProvider featureProvider)
+        public async Task SetProviderAsync(FeatureProvider? featureProvider)
         {
             this._eventExecutor.RegisterDefaultFeatureProvider(featureProvider);
             await this._repository.SetProvider(featureProvider, this.GetContext()).ConfigureAwait(false);
@@ -80,6 +80,10 @@ public void SetProvider(string clientName, FeatureProvider featureProvider)
         /// <param name="featureProvider">Implementation of <see cref="FeatureProvider"/></param>
         public async Task SetProviderAsync(string clientName, FeatureProvider featureProvider)
         {
+            if (string.IsNullOrWhiteSpace(clientName))
+            {
+                throw new ArgumentNullException(nameof(clientName));
+            }
             this._eventExecutor.RegisterClientFeatureProvider(clientName, featureProvider);
             await this._repository.SetProvider(clientName, featureProvider, this.GetContext()).ConfigureAwait(false);
         }
@@ -138,8 +142,8 @@ public FeatureProvider GetProvider(string clientName)
         /// <param name="logger">Logger instance used by client</param>
         /// <param name="context">Context given to this client</param>
         /// <returns><see cref="FeatureClient"/></returns>
-        public FeatureClient GetClient(string name = null, string version = null, ILogger logger = null,
-            EvaluationContext context = null) =>
+        public FeatureClient GetClient(string? name = null, string? version = null, ILogger? logger = null,
+            EvaluationContext? context = null) =>
             new FeatureClient(name, version, logger, context);
 
         /// <summary>
@@ -200,7 +204,7 @@ public void AddHooks(IEnumerable<Hook> hooks)
         /// Sets the global <see cref="EvaluationContext"/>
         /// </summary>
         /// <param name="context">The <see cref="EvaluationContext"/> to set</param>
-        public void SetContext(EvaluationContext context)
+        public void SetContext(EvaluationContext? context)
         {
             this._evaluationContextLock.EnterWriteLock();
             try

src/OpenFeature/Error/FeatureProviderException.cs

@@ -20,7 +20,7 @@ public class FeatureProviderException : Exception
         /// <param name="errorType">Common error types <see cref="ErrorType"/></param>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public FeatureProviderException(ErrorType errorType, string message = null, Exception innerException = null)
+        public FeatureProviderException(ErrorType errorType, string? message = null, Exception? innerException = null)
             : base(message, innerException)
         {
             this.ErrorType = errorType;

src/OpenFeature/Error/FlagNotFoundException.cs

@@ -15,7 +15,7 @@ public class FlagNotFoundException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public FlagNotFoundException(string message = null, Exception innerException = null)
+        public FlagNotFoundException(string? message = null, Exception? innerException = null)
             : base(ErrorType.FlagNotFound, message, innerException)
         {
         }

src/OpenFeature/Error/GeneralException.cs

@@ -15,7 +15,7 @@ public class GeneralException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public GeneralException(string message = null, Exception innerException = null)
+        public GeneralException(string? message = null, Exception? innerException = null)
             : base(ErrorType.General, message, innerException)
         {
         }

src/OpenFeature/Error/InvalidContextException.cs

@@ -15,7 +15,7 @@ public class InvalidContextException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public InvalidContextException(string message = null, Exception innerException = null)
+        public InvalidContextException(string? message = null, Exception? innerException = null)
             : base(ErrorType.InvalidContext, message, innerException)
         {
         }

src/OpenFeature/Error/ParseErrorException.cs

@@ -15,7 +15,7 @@ public class ParseErrorException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public ParseErrorException(string message = null, Exception innerException = null)
+        public ParseErrorException(string? message = null, Exception? innerException = null)
             : base(ErrorType.ParseError, message, innerException)
         {
         }

src/OpenFeature/Error/ProviderNotReadyException.cs

@@ -15,7 +15,7 @@ public class ProviderNotReadyException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public ProviderNotReadyException(string message = null, Exception innerException = null)
+        public ProviderNotReadyException(string? message = null, Exception? innerException = null)
             : base(ErrorType.ProviderNotReady, message, innerException)
         {
         }

src/OpenFeature/Error/TargetingKeyMissingException.cs

@@ -15,7 +15,7 @@ public class TargetingKeyMissingException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public TargetingKeyMissingException(string message = null, Exception innerException = null)
+        public TargetingKeyMissingException(string? message = null, Exception? innerException = null)
             : base(ErrorType.TargetingKeyMissing, message, innerException)
         {
         }

src/OpenFeature/Error/TypeMismatchException.cs

@@ -15,7 +15,7 @@ public class TypeMismatchException : FeatureProviderException
         /// </summary>
         /// <param name="message">Exception message</param>
         /// <param name="innerException">Optional inner exception</param>
-        public TypeMismatchException(string message = null, Exception innerException = null)
+        public TypeMismatchException(string? message = null, Exception? innerException = null)
             : base(ErrorType.TypeMismatch, message, innerException)
         {
         }