Exception in thread MSKeyAction:
 Traceback (most recent call last):
   File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
     self.run()
   File "/usr/lib/python3.5/threading.py", line 862, in run
     self._target(*self._args, **self._kwargs)
   File "/home/immae/.local/lib/python3.5/site-packages/transitions/core.py", line 238, in trigger
     return self.machine._process(f)
   File "/home/immae/.local/lib/python3.5/site-packages/transitions/core.py", line 568, in _process
     self._transition_queue[0]()
   File "/home/immae/.local/lib/python3.5/site-packages/transitions/extensions/nesting.py", line 118, in _trigger
     if t.execute(event):
   File "/home/immae/.local/lib/python3.5/site-packages/transitions/core.py", line 167, in execute
     machine._callback(func, event_data)
   File "/home/immae/.local/lib/python3.5/site-packages/transitions/core.py", line 547, in _callback
     func(*event_data.args, **event_data.kwargs)
   File "/home/immae/projets/music_sampler/music_sampler/key.py", line 212, in run_actions
     self.list_actions()
   File "/home/immae/projets/music_sampler/music_sampler/key.py", line 280, in list_actions
     action_descriptions)
   File "/home/immae/projets/music_sampler/music_sampler/app_blocks/actionlist.py", line 28, in update_list
     self.action_list = action_list
   File "kivy/properties.pyx", line 408, in kivy.properties.Property.__set__ (/tmp/pip-build-s6urhuix/kivy/kivy/properties.c:5147)
   File "kivy/properties.pyx", line 733, in kivy.properties.ListProperty.set (/tmp/pip-build-s6urhuix/kivy/kivy/properties.c:10986)
   File "kivy/properties.pyx", line 446, in kivy.properties.Property.set (/tmp/pip-build-s6urhuix/kivy/kivy/properties.c:5908)
   File "kivy/properties.pyx", line 501, in kivy.properties.Property.dispatch (/tmp/pip-build-s6urhuix/kivy/kivy/properties.c:6572)
   File "kivy/_event.pyx", line 1224, in kivy._event.EventObservers.dispatch (/tmp/pip-build-s6urhuix/kivy/kivy/_event.c:13484)
   File "kivy/_event.pyx", line 1130, in kivy._event.EventObservers._dispatch (/tmp/pip-build-s6urhuix/kivy/kivy/_event.c:12686)
   File "/home/immae/projets/music_sampler/music_sampler/app_blocks/actionlist.py", line 43, in update_actionlist_icons
     icon_label = ActionListIcon(text=icon)
   File "/home/immae/projets/music_sampler/music_sampler/app_blocks/actionlist.py", line 49, in __init__
     super(ActionListIcon, self).__init__(**kwargs)
   File "/home/immae/.local/lib/python3.5/site-packages/kivy/uix/label.py", line 266, in __init__
     super(Label, self).__init__(**kwargs)
   File "/home/immae/.local/lib/python3.5/site-packages/kivy/uix/widget.py", line 320, in __init__
     Builder.apply(self, ignored_consts=self._kwargs_applied_init)
   File "/home/immae/.local/lib/python3.5/site-packages/kivy/lang.py", line 1970, in apply
     self._apply_rule(widget, rule, rule, ignored_consts=ignored_consts)
   File "/home/immae/.local/lib/python3.5/site-packages/kivy/lang.py", line 1982, in _apply_rule
     assert(rule not in self.rulectx)
 AssertionError