c# nullable reference types: narrowing of IEnumerable<T>? to IEnumerable<T>

[naighes]

Howdy!
Not sure if this falls into the known pitfalls of arrays, but I cannot "unwrap" IEnumerable<T>? to IEnumerable<T>.
Here's what I'm doing:

IEnumerable<string>? x = new List<string>();
var y = x ?? Enumerable.Empty<string>();

Anyway, it looks y is still of type IEnumerable<string>? rather than IEnumerable<string>, despite the usage of the null-coalescing operator... and cannot sort it out why.
Any hint?

PS. by the way, without type inference the compiler doesn't complain anymore:

IEnumerable<string>? x = new List<string>();
IEnumerable<string> y = x ?? Enumerable.Empty<string>(); // no warnings

[svick]

When you use var and initialize the variable with a non-nullable reference type, it starts as "nullable, but known to be not null". This is so that you could assign null to it later on. But the compiler understands that it's not null, so it will mostly treat it as non-nullable otherwise.