prepare_lookup_value should treat 0 as False for __isnull

[benjie@…]

In contrib.admin.util, there is a prepare_lookup_value function

In this function, there is a clause

if value.lower() in (, 'false'):

value = False

I think it should be

if value.lower() in (, 'false', '0'):

value = False

Note that in admin already converts a limit_choices_to={'aisnull': False} to aisnull=0 when formatting a query string for lookup on the remote model. Therefore, clearly it should also handle isnull=0 correctly. Currently the lookup popup box on remote model uses isnull=0 and does not actually filter.

See the following pull request

​https://github.com/django/django/pull/982