Cannot add new task

I try to add a new task.
Steps to reproduce:
- click on Tray icon, select Add new task
- select Task list, insert title, insert description, insert Due date, click OK
- window closes, but my task does not show up in the menu or the task list
- try to sync with google, I get this response

{'Authorization': 'OAuth ya29.AHES6ZTxCjHfffIgR4A7kwrmIUGsvLGx6sOxhZVwTAvHdpAHvywa2fg'}
<Response [200]>
Traceback (most recent call last):
  File "/usr/share/google-tasks-indicator/googletasksindicator.py", line 220, in sync
    new_task = gta.create_task( tasklist_id = task['tasklist_id'], title = task['title'], notes=task['notes'], iscompleted=task.get_completed(),due=due,data_completed=task['completed'])
UnboundLocalError: local variable 'due' referenced before assignment

My settings are like this:
a) Options tab
Task list -> one of my task list selected
Autostart -> on
Theme light -> on

b) Sync options
Tasks local only -> copy to external
Tasks external only -> copy to local
Tasks local and external only -> do none

c) Login
Allow acces to Google tasks -> on

BTW, it does add a new task list, but it multiplies it on sync. I have 2 task lists with the same name (the one I created last night). It should only create it again if it does not exist.