c# - Why doesn't obj ?? null cause an compiler warning -

In the case where the reference type has been processed with zero, why is not the compiler alert in the C # compiler? Is there a case where it makes sense?

  obj2 = obj ?? Zero;    
 
 
 Your example really does not understand, but something like this does;    d = a ?? B ?? C ?? Zero;   
 Here, I am saying that all three have to take unrestricted value, if they are all empty, then just be empty.