title: DFP AD Code (Javascript) causing PHP Notice: Undefined index Errors
body: <p>I've recently notice a large number of PHP "Undefined index" errors in my php logs. The errors all looked like this (but were for many different variables (this one is for gender) and different lines) and all are $_SESSION Variables:</p>
  
  <p>I think worked through the related site code to work out what was causing the errors. Finally I've found if I comment out the DFP AD Slots (Javascript - shown below) the errors stop occuring. (there are more slots - I've just shown one)</p>