File "electrum/gui/qt/main_window.py", line 2967, in closeEvent
  File "electrum/gui/qt/main_window.py", line 2984, in clean_up
  File "electrum/gui/qt/__init__.py", line 338, 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 262, in save_user_config