Exceptions for "Possible System.NullReferenceException"

This is not a big issue but when you have a call to System.Security.Principal.WindowsIdentity.GetCurrent() in an if-statement, R# says that GetCurrent() might return a possible System.NullReferenceException.

Is it possible to add exceptions to the "Possible System.NullReferenceException" for methods of which you are sure that will always return a valid object?