diff --git a/payments/models.py b/payments/models.py
index 2b7736db2..4e9a9ffdd 100644
--- a/payments/models.py
+++ b/payments/models.py
@@ -147,29 +147,32 @@ def get_user(self):
     def get_user_email(self):
         """ Get user email """
         try:
+            # Most common implementation
             return self.get_user().email
         except AttributeError:
-            return None
+            raise NotImplementedError()
 
     def get_user_first_name(self):
         """
-        Get user first name
+        Get user first name for purposes of the payment provider
         Used only by PayU provider for now
         """
         try:
+            # Most common implementation
             return self.get_user().first_name
         except AttributeError:
-            return None
+            raise NotImplementedError()
 
     def get_user_last_name(self):
         """
-        Get user last name
+        Get user last name for purposes of the payment provider
         Used only by PayU provider for now
         """
         try:
+            # Most common implementation
             return self.get_user().last_name
         except AttributeError:
-            return None
+            raise NotImplementedError()
 
     def get_renew_token(self):
         """