'Fixes the payload data.
Here converts string time from datetime obj'

def fix_payload(self, data):

    datetime_fields = ['starts_at', 'ends_at', 'schedule_published_on']
    for f in datetime_fields:
        if (f in data):
            data[f] = EVENT_POST[f].from_str(data.get(f))
    if data.get('call_for_papers'):
        for _ in ['start_date', 'end_date']:
            if (_ in data['call_for_papers']):
                data['call_for_papers'][_] = EVENT_CFS[_].from_str(data['call_for_papers'].get(_))
    return data
