'Test the measurement functions on fields with NULL values.'

@skipUnlessDBFeature('supports_null_geometries', 'has_Area_function', 'has_Distance_function')
def test_measurement_null_fields(self):

    SouthTexasZipcode.objects.create(name='78212')
    htown = SouthTexasCity.objects.get(name='Downtown    Houston')
    z = SouthTexasZipcode.objects.annotate(distance=Distance('poly', htown.point), area=Area('poly')).get(name='78212')
    self.assertIsNone(z.distance)
    self.assertIsNone(z.area)
