I've got a question. I tried to do a statement similar to the one below:

if(Session["variablename"] == true)
{//run code because variable was declared}
else
{}

however I am keep getting an internal server 500 code.

Is there a way to check to see if a variable was declared like:

Exist(Session["variablename"]) return boolean
IsNull(Session["variablename"]) return boolean