title: django-celery : TypeError: can only concatenate tuple (not "NoneType") to tuple
body: <p>I have recently started using rabbitmq and celery with django. i am using django-celery, django-celery-email and post office to send emails in async way. 
  After installing all these packages my settings.py looks like</p>
  
  <pre><code>INSTALLED_APPS = [
  #other apps
  'djcelery',
  'djcelery_email',
  'post_office'
  ]
  
  
  # setup celery
  import djcelery
  djcelery.setup_loader()
  
  # using post office as the default email backend 
  EMAIL_BACKEND = 'post_office.EmailBackend'
  # using djcelery's email backend as a backend for post office 
  
  POST_OFFICE_BACKEND = 'djcelery_email.backends.CeleryEmailBackend'
  
  POST_OFFICE = {
      'DEFAULT_PRIORITY' : 'now'
  }
  
  EMAIL_HOST = 'YOUR_HOST_NAME'
  EMAIL_HOST_USER = "YOUR_HOST_USER_NAME"
  EMAIL_PORT = 25  # default smtp port
  EMAIL_HOST_PASSWORD = "YOUR_HOST_USER_PASSWORD"
  EMAIL_USE_TLS = False
  DEFAULT_FROM_EMAIL = 'testing@example.com'
  </code></pre>
  
  <p>when i am trying to run django-celery via command</p>
  
  <pre><code>**python manage.py celeryd**
  </code></pre>
  
  <p>It is throughing below error</p>
  
  <pre><code>Traceback (most recent call last):
    File "manage.py", line 22, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
      utility.execute()
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 356, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 206, in fetch_command
      klass = load_command_class(app_name, subcommand)
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 40, in load_command_class
      module = import_module('%s.management.commands.%s' % (app_name, name))
    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/djcelery/management/commands/celeryd.py", line 16, in &lt;module&gt;
      class Command(CeleryCommand):
    File "/home/ubuntu/edyodavirtual/local/lib/python2.7/site-packages/djcelery/management/commands/celeryd.py", line 20, in Command
      worker.get_options() +
  TypeError: can only concatenate tuple (not "NoneType") to tuple
  </code></pre>
  
  <p>Anyone here help me to fix this</p>