This repository demonstrates a bug in the 05/14/18 C# Nullable Reference Types Preview with Visual Studio 2017 15.7.1. It corresponds to dotnet/roslyn#27009.

Project Setup

The project features a handful of properties on Program that return non-null references using the null coalescing operator:

Property	Description
FooProperty	Lazy-initializes a field inside the right-hand side of a null coalescing operator
FooProperty2	"Lazy-initializes" a local variable inside the right-hand side of a null coalescing operator
FooProperty3	Returns a field or a new instance using a null coalescing operator
FooProperty4	Lazy-initializes a field without using the null coalescing operator

(FooProperty2 exists to make sure this problem isn't related to dotnet/roslyn#9978.)

Additionally, there are static and non-static versions of the properties.

Actual Behavior

The compiler reports the following warning for FooProperty and FooProperty2:

warning CS8603: Possible null reference return.

Additionally, the warning is also reported for FooProperty4, but only for the static version.

Expected Behavior

No warning is reported because the assignment causes the _foo field/ret variable to be initialized with a non-null value.