How can a C# parameter with default value be null?

Question

The code shown below shows a method Get which gets string search with default value: "".

How can the value possibly be null when search has a non-null default value and is never changed?

Answer 1

How can the value possibly be null when search has a non-null default value and is never changed?

If you explicitly pass null to the method (or a variable which is null), the default is not used.

The default value is only used if you call the method without the parameter in place, in which case the compiler "fills in" the default value for you. If you call the method with something, including null or a object variable which is null, you will get a null value there.