docs: def _validate_param(rtype, fields):
      """ Ensure the sparse fields exists on the models """
  
      try:
          # raises ValueError if not found
          model = rtype_to_model(rtype)
          model_fields = model.all_fields
      except ValueError:
          raise InvalidQueryParams(**{
              'detail': 'The fields query param provided with a '
                        'field type of "%s" is unknown.' % rtype,
              'links': LINK,
              'parameter': PARAM,
          })
  
      for field in fields:
          if field not in model_fields:
              raise InvalidQueryParams(**{
                  'detail': 'The fields query param "TYPE" of "%s" '
                            'is not possible. It does not have a field '
                            'by the name of "%s".' % (rtype, field),
                  'links': LINK,
                  'parameter': PARAM,
              })