File "/usr/local/lib/python3.6/dist-packages/electrum/gui/qt/main_window.py", line 3025, in closeEvent
  File "/usr/local/lib/python3.6/dist-packages/electrum/gui/qt/main_window.py", line 3032, in clean_up
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 142, in set_key
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 151, in _set_key_in_user_config
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 231, in save_user_config