Nullable String

Error:
The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'

Problem:
- I have a function that I want to pass data that gets data from ...
- What's C# problme with nullable string ...
- Why no support for nullable string in C#
- C# have a problem with passing nullable string ...
- public void test(string? x){} has ERROR
- public void test(Nullable x){} has ERROR

Solution:
:-D System.String is a reference type and it is nullable. :-)