code: def _assert_relation_does_not_exists(self):
          
          relations = self.database._relations[self.related_to]
          existing = [r for r in relations if r[2] == self.related_name]
          if existing:
              error = ("The related name defined for the field '%s.%s', named '%s', already exists "
                       "on the model '%s' (tied to the field '%s.%s')")
              raise ImplementationError(error % (self._model.__name__, self.name, self.related_name,
                                        self.related_to, existing[0][1], existing[0][0]))
docs: Check if a relation with the current related_name doesn't already exists
          for the related model