Missing code signature when invoking methods on compiler constants

[SirIntruder]

VS Code version: 1.26.0
C# Extension version: 16 beta

When completing methods on compiler constants, like:

var x1 = 3.ToString("X"); 
var x2 = "foo".IndexOf('o');

VSCode never displays signature help. IndexOf/ToString() are displayed in auto complete list, but once typed, signature help is not shown when pressing ctrl+shift+space inside argument parens.

If 3 or "foo" are assigned to variables, everything works as expected.

[SirIntruder]

PR with the fix is merged into omnisharp, issue can be closed.