File "/usr/local/lib/python3.6/dist-packages/electrum/gui/qt/main_window.py", line 3119, in closeEvent
    self.clean_up()
  File "/usr/local/lib/python3.6/dist-packages/electrum/gui/qt/main_window.py", line 3128, in clean_up
    self.config.set_key("is_maximized", self.isMaximized())
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 149, in set_key
    self._set_key_in_user_config(key, value, save)
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 158, in _set_key_in_user_config
    self.save_user_config()
  File "/usr/local/lib/python3.6/dist-packages/electrum/simple_config.py", line 239, in save_user_config
    f.write(s)