# No Subject header

This rule matches if the message has no `Subject:` header, or if the header is the empty string when stripped.

    >>> from mailman.app.lifecycle import create_list
    >>> mlist = create_list('_xtest@example.com')
    >>> from mailman.config import config
    >>> rule = config.rules['no-subject']
    >>> print(rule.name)
    no-subject

A message with a non-empty subject does not match the rule.

    >>> from mailman.testing.helpers import (specialized_message_from_string
    ...   as message_from_string)
    >>> msg = message_from_string("""\
    ... From: aperson@example.org
    ... To: _xtest@example.com
    ... Subject: A posted message
    ...
    ... """)
    >>> rule.check(mlist, msg, {})
    False

Delete the `Subject:` header and the rule matches.

    >>> del msg['subject']
    >>> rule.check(mlist, msg, {})
    True

Even a `Subject:` header with only whitespace still matches the rule.

    >>> msg['Subject'] = '    '
    >>> rule.check(mlist, msg, {})
    True