get_completions() needing an external command

Hello all,
my completion workflow differs from the one shown in the examples: i need to execute a command taking for argument the word and returning the list of possible completions.

I don't succeed to make it work because I don't get the async functionning of the module. While debugging, I see that my script tries to execute the command with word='' instead of the letters I typed in the prompt.

class MyCompleter(Completer):
    def get_completions(self, document, complete_event):
      word = document.get_word_before_cursor()
      completion_propositions = external_command(word)
      for proposition in completion_propositions:
        yield Completion(proposition, start_position=-len(word))

Start with the get_completions example shown in the issue, especially document.get_word_before_cursor and the external_command call. Reproduce the completion flow while typing and trace why the command receives an empty word; the work is done when the typed word is passed to the external command and its returned propositions are yielded.