diff --git a/Directory.Build.props b/Directory.Build.props
index 6b9ec43..9edb06f 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -3,10 +3,11 @@
   <PropertyGroup>
     <CurrentPreviewTfm>net8.0</CurrentPreviewTfm>
     <!--<IncludePreview>true</IncludePreview>-->
-    <IncludePreview Condition=" '$(IncludePreview)' == ''">false</IncludePreview>
+    <IncludePreview Condition="'$(IncludePreview)' == ''">false</IncludePreview>
     <LangVersion>latest</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <WarningsAsErrors>nullable</WarningsAsErrors>
   </PropertyGroup>
 
   <PropertyGroup>
@@ -19,7 +20,7 @@
 
   <ItemGroup>
     <!--
-      The .NET Framework target doesn't seem to like this implicit using so we 
+      The .NET Framework target doesn't seem to like this implicit using so we
       have to bring it in for each file, so might as well remove it for .NET targets too.
     -->
     <Using Remove="System.Net.Http" />
diff --git a/src/Sdk/Models/AddAliasRequest.cs b/src/Sdk/Models/AddAliasRequest.cs
index 5230f6e..ed07275 100644
--- a/src/Sdk/Models/AddAliasRequest.cs
+++ b/src/Sdk/Models/AddAliasRequest.cs
@@ -24,6 +24,7 @@ private AddAliasRequest(string userId, bool hashing = true)
     {
         UserId = userId ?? throw new ArgumentNullException(nameof(userId));
         Hashing = hashing;
+        Aliases = new HashSet<string>();
     }
 
     public string UserId { get; }