fix by on last statement

kfet/views.py

@@ -858,6 +858,7 @@ def kpsul_checkout_data(request, pk):
             last_statement,
             fields=['id', 'at', 'balance_new', 'balance_old', 'by']
         )
+        last_statement_data['by'] = str(last_statement.by)
         # ``at`` is not editable, so skipped by ``model_to_dict``
         last_statement_data['at'] = last_statement.at
         data['laststatement'] = last_statement_data