File "electrum\gui\qt\main_window.py", line 3171, in closeEvent
  File "electrum\gui\qt\main_window.py", line 3192, in clean_up
  File "electrum\gui\qt\__init__.py", line 284, in close_window
  File "electrum\simple_config.py", line 294, in save_last_wallet
  File "electrum\simple_config.py", line 149, in set_key
  File "electrum\simple_config.py", line 158, in _set_key_in_user_config
  File "electrum\simple_config.py", line 238, in save_user_config