c# - Creating nullable class -

how create nullable (?) class in c#? like:

public class hello1 {   public int property1 { get; set; } }  public class hello2 {  public hello1? property2 { get; set; } //hello1 should work when has "?" } 

i wanna make hello1 class take form "hello1?" if needed.

you don't need create nullable type reference types. they're nullable. need value types int, bool, decimal, etc...