code: def on_accel_cleared(self, cellrendereraccel, path):
          
          dconf_path = self.store[path][HOTKET_MODEL_INDEX_DCONF]
  
          if dconf_path == "show-hide":
              # cannot disable 'show-hide' hotkey
              log.warn("Cannot disable 'show-hide' hotkey")
              self.settings.keybindingsGlobal.set_string(dconf_path, old_accel)
          else:
              self.store[path][HOTKET_MODEL_INDEX_HUMAN_ACCEL] = ""
              self.store[path][HOTKET_MODEL_INDEX_ACCEL] = "None"
              if dconf_path == "show-focus":
                  self.settings.keybindingsGlobal.set_string(dconf_path, 'disabled')
              else:
                  self.settings.keybindingsLocal.set_string(dconf_path, 'disabled')
docs: If the user tries to clear a keybinding with the backspace
          key this callback will be called and it just fill the model
          with an empty key and set the 'disabled' string in dconf path.