Fixed #3501 -- Fixed date filtering in querysets for nullable date fields. Only

        return query % tuple("?" * num_params)

def _sqlite_extract(lookup_type, dt):

    if dt is None:

        return None

    try:

        dt = util.typecast_timestamp(dt)

    except (ValueError, TypeError):

    name = models.CharField(max_length=60)

class Party(models.Model):

    when = models.DateField()

    when = models.DateField(null=True)

class Event(models.Model):

    when = models.DateTimeField()

>>> [p.when for p in Party.objects.filter(when__year='1998')]

[datetime.date(1998, 12, 31)]

# Date filtering was failing with NULL date values in SQLite (regression test

# for #3501, amongst other things).

>>> _ = Party.objects.create()

>>> p = Party.objects.filter(when__month=1)[0]

>>> p.when

datetime.date(1999, 1, 1)

>>> l = Party.objects.filter(pk=p.pk).dates("when", "month")

>>> l[0].month == 1

True

# Check that get_next_by_FIELD and get_previous_by_FIELD don't crash when we

# have usecs values stored on the database

#