Added one more test

Added one more test to avoid mistake with backward compatibility

gluon/tests/test_storage.py

@@ -138,6 +138,8 @@ class TestList(unittest.TestCase):
         self.assertEqual(a(3, cast=int), 1234)
         a.append('x')
         self.assertRaises(HTTP, a, 4, cast=int)
+        b = List()
+        self.assertEqual(b(0, cast=int, default=None), None)
 
 
 if __name__ == '__main__':