Fix issue where reports page was not loaded if a refunded charge did not have a PO set.  Since there was no PO, the value of the metadata field was "nil", not "string" in the interface conversion.  This threw an error and resulted in the reports page not loading.  Just removed the PO field from the returned data since it was not used anyway (was not shown in gui).
Fix issue where reports page was not loaded if a refunded charge did not have a PO set.  Since there was no PO, the value of the metadata field was "nil", not "string" in the interface conversion.  This threw an error and resulted in the reports page not loading.  Just removed the PO field from the returned data since it was not used anyway (was not shown in gui).

coreymgilmore/stripe-appengine-frontend,coreymgilmore/stripe-appengine-frontend,coreymgilmore/stripe-appengine-frontend