Merge pull request #41579 from sharwell/enable-nrt

Enable nullable reference types in projects that do not target netcoreapp3.1

eng/targets/Imports.targets

@@ -24,7 +24,7 @@
       This condition will be evaluated multiple times in multi-targeted projects hence need to be careful
       to only set in the inner builds, not the outer build where only $(TargetFrameworks) is defined.
     -->
-    <DisableNullableWarnings Condition="'$(DisableNullableWarnings)' == '' AND '$(TargetFramework)' != '' AND '$(TargetFramework)' != 'netcoreapp3.1'">true</DisableNullableWarnings>
+    <DisableNullableWarnings Condition="'$(DisableNullableWarnings)' == '' AND $(TargetFrameworks.Contains('netcoreapp3.1')) AND '$(TargetFramework)' != '' AND '$(TargetFramework)' != 'netcoreapp3.1'">true</DisableNullableWarnings>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(DisableNullableWarnings)' == 'true'">

src/ExpressionEvaluator/Core/Source/ExpressionCompiler/EEMetadataReferenceResolver.cs

@@ -50,7 +50,7 @@ internal sealed class EEMetadataReferenceResolver : MetadataReferenceResolver
         public override ImmutableArray<PortableExecutableReference> ResolveReference(string reference, string? baseFilePath, MetadataReferenceProperties properties)
             => throw ExceptionUtilities.Unreachable;
 
-        public override bool Equals(object other)
+        public override bool Equals(object? other)
             => throw ExceptionUtilities.Unreachable;
 
         public override int GetHashCode()

src/ExpressionEvaluator/Core/Source/ExpressionCompiler/EvaluationContextBase.cs

@@ -155,7 +155,7 @@ public override bool Equals(Diagnostic? obj)
                 throw new NotImplementedException();
             }
 
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
             {
                 throw new NotImplementedException();
             }