Trailing comma gives wrong warning: msgid already exists with a different default

[mauritsvanrees]

Add a Python file test.py with this:

one = _('Hello')
two = _(
    'Hello',
)

Rebuild/create a pot file and you get a warning:

$ i18ndude rebuild-pot -p test.pot -c test test.py 
Warning: msgid 'Hello' in test.py:2 already exists with a different default (bad: , should be: None)
The references for the existent value are:
test.py:1

It is only a warning, the resulting pot file is okay:

#: test.py:1
msgid "Hello"
msgstr ""

But the warning is wrong: the trailing comma does not mean we have a default value of , instead of None.