Error adding task without deadline

[mikeshultz]

Traceback:
File "/var/www/venvs/doto/lib/python3.4/site-packages/django/core/handlers/base.py" in get_response
  132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/var/www/venvs/doto/lib/python3.4/site-packages/django/views/generic/base.py" in view
  71.             return self.dispatch(request, *args, **kwargs)
File "/var/www/venvs/doto/lib/python3.4/site-packages/django/views/generic/base.py" in dispatch
  89.         return handler(request, *args, **kwargs)
File "./doto/views.py" in post
  93.                 deadline = datetime_to_iso(request.POST.get('deadline')),
File "./doto/utils.py" in datetime_to_iso
  49.         datetime.strptime(dt, '%Y-%m-%d')
File "/usr/local/lib/python3.4/_strptime.py" in _strptime_datetime
  507.     tt, fraction = _strptime(data_string, format)
File "/usr/local/lib/python3.4/_strptime.py" in _strptime
  344.                          (data_string, format))

Exception Type: ValueError at /task/
Exception Value: time data '' does not match format '%Y-%m-%d'