Blank admin filter for Django 1.4+.

admin.py

from django.contrib import admin


class BlankFilter(admin.SimpleListFilter):
    """Abstract base class for filtering blank fields.

    To use define a subclass that defines title and parameter_name fields:

        class ConcreteBlankFilter(BlankFilter):
            title = "some title"
            parameter_name = "model_field_name"

    This has been inspired (read "almost an exact copy of") this solution
    at StackOverflow: http://stackoverflow.com/a/9593302/519510

    """
    title = ''
    parameter_name = ''

    def lookups(self, request, model_admin):
        return (
            ('1', _('Has value'), ),
            ('0', _('Empty value'), ),
        )

    def queryset(self, request, queryset):
        kwargs = {
            unicode(self.parameter_name): '',
        }
        if self.value() == '0':
            return queryset.filter(**kwargs)
        if self.value() == '1':
            return queryset.exclude(**kwargs)
        return queryset


class ConcreteBlankFilter(BlankFilter):
    title = "this filter is usable in "
    parameter_name = "model_field_name" # model_field_name should correspond to 
                                        # a field with blank=True


class SomeModelAdmin(admin.ModelAdmin):
    list_filter = [ConcreteBlankFilter]