'An rport setting of None should insert the parameter with no value.'

def test_rport(self):

    v = sip.Via('foo.bar', rport=None)
    self.assertEqual(v.toString(), 'SIP/2.0/UDP    foo.bar:5060;rport')
    self.assertTrue(v.rportRequested)
    self.assertIsNone(v.rportValue)
