string.Empty vs null.Which one do you use?

Question

Recently a colleague at work told me not to use string.Empty when setting a string variable but use null as it pollutes the stack?

He says

Answer 1

It's been answered to death, but null means no value, not initialized. string.Empty means "" (a blank string) as it is stated on MSDN.

The safest way to check for an empty or null string is using string.IsNullOrEmpty.