In order to support codebases that have been upgraded to use C# 8´s new nullable ref types feature, it would be great if you could annotate all methods that may return null, such as FirstOrDefaultAsync, with [return: MaybeNull].

See https://docs.microsoft.com/en-us/dotnet/csharp/nullable-attributes#specify-post-conditions-maybenull-and-notnull for more information.