What is the best way to determine a session variable is null or empty in C#?

Question

What is the best way to check for the existence of a session variable in ASP.NET C#?

I like to use String.IsNullOrEmpty() works for strings and wonder

Answer 1

in this way it can be checked whether such a key is available

if (Session.Dictionary.ContainsKey("Sessionkey"))  --> return Bool