Improving non-nullable reference types handling

A few weeks ago I started using non-nullable reference types - a new C# language feature which was shipped with version 8.0. It wasn’t a completely new experience for me, because I was working before on projects that were heavily utilizing [NotNull] and [CanBeNull] Resharper annotations. The way how non-nullable types are handled by Roslyn seems to be a little more complex in comparison to Resharper - there are around 40 different diagnostics related to this area.