'get_choices() works with empty iterators.'

def test_empty_iterator_choices(self):

    self.assertEqual(WhizIterEmpty(c='a').c, 'a')
    self.assertEqual(WhizIterEmpty(c='b').c, 'b')
    self.assertIsNone(WhizIterEmpty(c=None).c)
    self.assertEqual(WhizIterEmpty(c='').c, '')
