File "electrum\gui\qt\main_window.py", line 3256, in closeEvent
  File "electrum\gui\qt\main_window.py", line 3277, in clean_up
  File "electrum\gui\qt\__init__.py", line 305, in close_window
  File "electrum\simple_config.py", line 299, in save_last_wallet
  File "electrum\simple_config.py", line 154, in set_key
  File "electrum\simple_config.py", line 163, in _set_key_in_user_config
  File "electrum\simple_config.py", line 243, in save_user_config