When you touch variables, you always need to know their values and even more their data type. The session manager is the tool to give you this kind of information.
In the Administration Tool, open the repository in online mode, Menu / Manage / Sessions. You will see then the values of the variable in the bottom of the windows in the tab named variable :
You could not find the value of a session variable modified by the initialization of a request variable because they don't have the same scope. The request variable is available only for a dashboard/answer while the session variable is valid for the whole user session.
Programmatically, by using the NQSGetSessionValues procedure, you can get their values.
The value in the session manager is likely NULL ?