AttributeError: 'list' object has no attribute 'add'

a new error is rised:

```
Traceback (most recent call last):
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/arbiter.py", line 507, in spawn_worker
worker.init_process()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/workers/ggevent.py", line 192, in init_process
super(GeventWorker, self).init_process()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/workers/base.py", line 118, in init_process
self.wsgi = self.app.wsgi()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/app/base.py", line 67, in wsgi
self.callable = self.load()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/app/wsgiapp.py", line 65, in load
return self.load_wsgiapp()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/app/wsgiapp.py", line 52, in load_wsgiapp
return util.import_app(self.app_uri)
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gunicorn/util.py", line 355, in import_app
__import__(module)
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gevent/builtins.py", line 58, in __import__
result = _import(*args, **kwargs)
File "/mnt/usb500G/pyProjectsEnv/proGeekAPI/proGeekAPI/wsgi.py", line 16, in
application = get_wsgi_application()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/django/core/wsgi.py", line 14, in get_wsgi_application
django.setup()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/django/__init__.py", line 18, in setup
apps.populate(settings.INSTALLED_APPS)
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/django/apps/registry.py", line 115, in populate
app_config.ready()
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/navutils/apps.py", line 10, in ready
menu.registry.autodiscover(settings.INSTALLED_APPS)
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/persisting_theory/registries.py", line 107, in autodiscover
module = __import__(package)
File "/mnt/usb500G/pyProjectsEnv/proGeekEnv/local/lib/python2.7/site-packages/gevent/builtins.py", line 58, in __import__
result = _import(*args, **kwargs)
File "/mnt/usb500G/pyProjectsEnv/proGeekAPI/dashboard_main/menu.py", line 20, in
blog.children.add(
AttributeError: 'list' object has no attribute 'add'
```

Menu file:

```
menu.py
from navutils import menu

main_menu = menu.Menu('main')
menu.register(main_menu)

# will be shown to everybody
blog = menu.Node(id='blog', label='Blog', pattern_name='blog:index')
main_menu.register(blog)

# nodes created with a pattern_name argument will use django reverse
#assert blog.get_url() == '/blog'

# if you want to disable reversion, use the url argument
django = menu.Node(id='django',
label='Django project',
url='http://djangoproject.com',
link_attrs={'target': '_blank'})

# Each node instance can accept an arbitrary number of children
blog.children.add(
menu.Node(id='last_entries',
label='Last entries',
pattern_name='blog:last_entries')
)
blog.children.add(
menu.Node(id='archives', label='Archives', pattern_name='blog:archives')
)

# will be shown to anonymous users only
login = menu.AnonymousNode(id='login',
label='Login',
pattern_name='accounts_login',
link_attrs={'class': 'big-button'})
main_menu.register(login)

# will be shown to authenticated users only
logout = menu.AuthenticatedNode(id='logout',
label='Logout',
pattern_name='accounts_logout')
main_menu.register(logout)
```