File "electrum\gui\qt\main_window.py", line 3018, in closeEvent
  File "electrum\gui\qt\main_window.py", line 3035, in clean_up
  File "electrum\gui\qt\__init__.py", line 336, in close_window
  File "electrum\simple_config.py", line 311, in save_last_wallet
  File "electrum\simple_config.py", line 160, in set_key
  File "electrum\simple_config.py", line 169, in _set_key_in_user_config
  File "electrum\simple_config.py", line 261, in save_user_config