Save state in db editor doesn't work

[PiispaH]

Pressing Save state... from the context menu:

Traceback (most recent call last):
  File "C:\spine-toolbox\spinetoolbox\spine_db_editor\widgets\custom_qgraphicsviews.py", line 414, in _save_state
    self._spine_db_editor.save_graph_data(name)
  File "C:\spine-toolbox\spinetoolbox\spine_db_editor\widgets\graph_view_mixin.py", line 465, in save_graph_data
    db_map_graph_data = self._get_db_map_graph_data()
  File "C:\spine-toolbox\spinetoolbox\spine_db_editor\widgets\graph_view_mixin.py", line 461, in _get_db_map_graph_data
    db_map_graph_data[db_map] = json.dumps(graph_data)
  File "C:\AppData\Local\Programs\Python\Python39\lib\json\__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "C:\AppData\Local\Programs\Python\Python39\lib\json\encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "C:\AppData\Local\Programs\Python\Python39\lib\json\encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "C:\AppData\Local\Programs\Python\Python39\lib\json\encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type TempId is not JSON serializable