code: def clean(self):
          
          if self.lookup == '?':  # Randomly sort
              return
          else:
              lookups = self.lookup.split(LOOKUP_SEP)
              opts = self.model_def.model_class()._meta
              valid = True
              while len(lookups):
                  lookup = lookups.pop(0)
                  try:
                      field = opts.get_field(lookup)
                  except FieldDoesNotExist:
                      valid = False
                  else:
                      if isinstance(field, models.ForeignKey):
                          opts = get_remote_field_model(field)._meta
                      elif len(lookups):  # Cannot go any deeper
                          valid = False
                  finally:
                      if not valid:
                          msg = _("This field doesn't exist")
                          raise ValidationError({'lookup': [msg]})
docs: Make sure the lookup makes sense