drf-spectacular: AssertionError Serializer

i have an serializer who give me an exception, follow my traceback:

File "./manage.py", line 17, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line
381, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line
375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 323,
 in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 364,
 in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/management/commands/specta
cular.py", line 44, in handle
    schema = generator.get_schema(request=None, public=True)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py", line 161,
in get_schema
    paths=self.parse(request, public),
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py", line 141,
in parse
    operation = view.schema.get_operation(path, path_regex, method, self.registry)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 77, in g
et_operation
    operation['responses'] = self._get_response_bodies()
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 822, in
_get_response_bodies
    return {'200': self._get_response_for_code(response_serializers)}
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 847, in
_get_response_for_code
    component = self.resolve_serializer(serializer, 'response')
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 398, in
_map_serializer_field
    component = self.resolve_serializer(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 403, in
_map_serializer_field
    component = self.resolve_serializer(field.child, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 403, in
_map_serializer_field
    component = self.resolve_serializer(field.child, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 398, in
_map_serializer_field
    component = self.resolve_serializer(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 403, in
_map_serializer_field
    component = self.resolve_serializer(field.child, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 919, in
resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 580, in
_map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 639, in
_map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 403, in
_map_serializer_field
    component = self.resolve_serializer(field.child, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 907, in
resolve_serializer
    assert is_serializer(serializer)
AssertionError