Object reference not set to an instance of an object. with IDataReader

Question

I have some code that is supposed to connect with a database and populate some fields with existing information that is on the table.

I have run into the Object refrence not set to an instance of an object on the line with my IDataReader

IDataReader dr0 = DB.GetRS("SELECT * FROM StorefrontTheme as st 
INNER JOIN Store as str 
ON st.ThemeID = str.ThemeID WHERE CustomerID = '" 
+ Session["CustomerID"].ToString() + "'");

If there os any additional information needed I will supply it

Thank you

The Problem was my session variable.. I completely forgot I was no longer using

session["CustomerID"]

Again thank you

Answer 1

As mentioned, by both posters, CustomerID was coming back null