code: def get_multiple_choices_required(self):
          
          errors = []
          if self.required:
              for key, msg in self.error_messages.items():
                  if key == 'required':
                      errors.append(('$error.required', msg))
          return errors
docs: Add only the required message, but no 'ng-required' attribute to the input fields,
          otherwise all Checkboxes of a MultipleChoiceField would require the property "checked".