human
Solve the following python programming problem given the following code:
def _test_plug(self, namespace = None, mtu = None) : 
    def device_exists(device, namespace = None) : 
        return device.startswith ('brq') 
root_veth = mock.Mock () 
    ns_veth = mock.Mock () 
    self.ip ().add_veth = mock.Mock (return_value = (root_veth, ns_veth)) 
    self.device_exists.side_effect = device_exists 
    br = interface.BridgeInterfaceDriver (self.conf) 
    mac_address = 'aa:bb:cc:dd:ee:ff' 
    br.plug ('01234567-1234-1234-99', 'port-1234', 'ns-0', mac_address, namespace = ip_calls) 
    ip_calls = [mock.call (), mock.call ().add_veth ('tap0', 'ns-0', namespace2 = namespace)] 
    ns_veth.assert_has_calls ([mock.call.link.set_address (mac_address)]) 
    if mtu : 
        ns_veth.assert_has_calls ([mock.call.link.set_mtu (mtu)]) 
        root_veth.assert_has_calls ([mock.call.link.set_mtu (mtu)]) 
self.ip.assert_has_calls (ip_calls) 
    root_veth.assert_has_calls ([mock.call.link.set_up ()]) 
    ns_veth.assert_has_calls ([mock.call.link.set_up ()]) 

    
    

    Fix the buggy line: br.plug ('01234567-1234-1234-99', 'port-1234', 'ns-0', mac_address, namespace = ip_calls)
assistant
#Here is Python program to fix the buggy line: br.

br.plug ('01234567-1234-1234-99', 'port-1234', 'ns-0', mac_address, namespace = namespace)