'Ensure None binding over async queries'

def test_async_binding(self):

    prepared = self.session.prepare('\n                                                INSERT    INTO    test3rf.test    (k,    v)    VALUES        (?,    ?)\n                                                ')
    self.assertIsInstance(prepared, PreparedStatement)
    future = self.session.execute_async(prepared, (873, None))
    future.result()
    prepared = self.session.prepare('\n                                                SELECT    *    FROM    test3rf.test    WHERE    k=?\n                                                ')
    self.assertIsInstance(prepared, PreparedStatement)
    future = self.session.execute_async(prepared, (873,))
    results = future.result()
    self.assertEqual(results[0].v, None)
