list_filter cannot filter nullable fields

[Bob Thomas]

I have a model with a FloatField that is nullable. I would like to filter models that have that field set to null, so I added it to list_filter in my ModelAdmin class. When I select the "None" option, I get an exception from get_db_prep_value because it's calling float(None). I tried modifying get_db_prep_value for FloatField to return None if value is None or "None", which got rid of the exception, but did not return any results.

Will attach a patch if I figure out how to fix this to return correct results.

ForeignKey fields that are nullable do not even display a None option in the filter, but I get a similar error trying to modify the query string to use None instead of an id.

[Matt McClanahan]

Dup of #8528

[Bob Thomas]

My main complaint here was that there is a "None" option displayed which raises an exception when clicked, so it's not really the same as #8528, which is asking for the addition of a none/null option. I attached a patch to that ticket that fixes this, though.