Expression tree should support optional parameters

[informatorius]

I wish expression tree compiler could support invocation with optional parameters.

To get rid of the error message CS0854: "An expression tree may not contain a call or invocation that uses optional arguments"

[garcipat]

I would highly support this. Especially for CancellationTokens in async methods it would be nice when mocking not requireing to provide It.IsAny() everywhere when using Moq