Only show key_fields in error message
Only show key_fields in error message

This caused a crash when GET, POST, and context were added to
the django_args by the decorators.

Patch by: Sverre Rabbelier

MatthewWilkes/mw4068-packaging,MatthewWilkes/mw4068-packaging,MatthewWilkes/mw4068-packaging,MatthewWilkes/mw4068-packaging