Nullability annotations are wrong

[tom-englert]

Both TestCode and FixedCode properties accept null, but are marked as not-null

roslyn-sdk/src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.Analyzer.Testing/AnalyzerTest`1.cs

Lines 96 to 105 in d4e8061

	public string TestCode
	{
	set
	{
	if (value != null)
	{
	TestState.Sources.Add(value);
	}
	}
	}

[sharwell]

Why would a user need to assign null here? Seems like we would instead keep the current annotations, and over time if/when a user is assigning null and enables nullable reference types, they would be discouraged from that practice.

[tom-englert]

Just to be able to continue using this when nullable is enabled:

public class AnalyzerTest<TAnalyzer> : CSharpAnalyzerTest<TAnalyzer, Verifier>
    where TAnalyzer : DiagnosticAnalyzer, new()
{
    public AnalyzerTest(string? source = null)
    {
        TestCode = source;
        ReferenceAssemblies = ReferenceAssemblies.Net.Net60;
    }
}