broke modeladmin tests
|Reported by:||Ivan Giuliani||Owned by:||Ivan Giuliani|
|Severity:||Keywords:||modeladmin, admin, validationerror|
|Has patch:||yes||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
 fixed a wrong error message being thrown when admin prepopulated_fields referred to a field that does not exist. However the tests has not been changed to reflect this. Attached patch fixes this issue.