def test_omittedOptionalArgumentDeserializesAsNone(self):
        """
        L{ListOf.fromBox} correctly reverses the operation performed by
        L{ListOf.toBox} for optional arguments.
        """
        stringList = amp.ListOf(amp.Integer(), optional=True)
        objects = {}
        stringList.fromBox(b'omitted', {}, objects, None)
        self.assertEqual(objects, {'omitted': None})

        L{ListOf.fromBox} correctly reverses the operation performed by
        L{ListOf.toBox} for optional arguments.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_amp.py