Decorator breaks down (metaclass bases cannot create 'NoneType' instances)

[rtubio]

With the following code:

from datetime import timedelta
import logging
from periodically.decorators import daily
from common import misc
from booking.models import operational, tle

logger = logging.getLogger(__name__)

@daily()
def update_operational_slots():
    logger.info("Populating OperationalSlots table, daily task execution!")
    operational.OperationalSlotsManager.populate_slots(
        start=misc.get_midnight()+timedelta(days=3), duration=timedelta(days=1)
    )

I get the following exception when launching the Django tests:

File "/home/rtubio/repositories/satnet-release-1/WebServices/booking/periodictasks.py", line 31, in <module>
@daily()
File "/home/rtubio/repositories/satnet-release-1/WebServices/__v_env/local/lib/python2.7/site-packages/periodically/decorators.py", line 20, in decorator register.simple_task(fn, schedule, backend=backend)
File "/home/rtubio/repositories/satnet-release-1/WebServices/__v_env/local/lib/python2.7/site-packages/periodically/__init__.py", line 46, in simple_task class DecoratedTask(PeriodicTask):
TypeError: Error when calling the metaclass bases cannot create 'NoneType' instances

Any ideas? Am I doing something wrong?