CLI error when called with no arguments

On the command line, when calling ./bin/mailman with no arguments results in this error message:

Traceback (most recent call last):
  File "/usr/local/src/mailman-bundler/venv-3.4/bin/mailman", line 9, in <module>
    load_entry_point('mailman==3.0.0', 'console_scripts', 'mailman')()
  File "/usr/local/src/mailman-bundler/venv-3.4/lib/python3.4/site-packages/mailman/bin/mailman.py", line 100, in main
    args.func(args)
AttributeError: 'Namespace' object has no attribute 'func'

Probably the "help" text should be displayed instead, but definitely this could be handled more gracefully.