AppConfigNotFoundError for dev_appserver.py on Django-nonrel and Google App Engine

I'm trying to clear my local db like explained in the docs

But when I try and run the dev_appserver.py --clear_datastore command I get google.appengine.tools.dev_appserver.AppConfigNotFoundError

dev_appserver.py --clear_datastore dennys
Traceback (most recent call last):
  File "/usr/local/bin/dev_appserver.py", line 76, in <module>
    run_file(__file__, globals())
  File "/usr/local/bin/dev_appserver.py", line 72, in run_file
    execfile(script_path, globals_)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver_main.py", line 687, in <module>
    sys.exit(main(sys.argv))
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver_main.py", line 575, in main
    appinfo, matcher = dev_appserver.LoadAppConfig(root_path, {})
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 4359, in LoadAppConfig
    raise AppConfigNotFoundError
google.appengine.tools.dev_appserver.AppConfigNotFoundError

You have to specify the directory of your application in the command line to dev_appserver.py.