为什么 networkmanager.WatchState 会恐慌？

Question

每当网络状态发生变化时，我都需要观察网络变化并设置一些路由规则（例如，如果接口重新启动，我需要再次设置 ip 路由表 b/c src 是动态的，因此我无法对其进行硬编码）。为了实现这一点，我正在尝试使用networkmanager包，但 WatchState 会出现恐慌。知道为什么吗？

package main

import(

    "flag"

    "os" 

    "launchpad.net/ubuntu-push/bus"

    "launchpad.net/ubuntu-push/bus/networkmanager"

    "launchpad.net/ubuntu-push/logger"

)

func main(){

    flag.Parse()

    lg := logger.NewSimpleLogger(os.Stderr, "info")

    endp := bus.SystemBus.Endpoint(networkmanager.BusAddress, lg)

    nm := networkmanager.New(endp, lg)

    watchState, cancel, err := nm.WatchState()

    if err !=nil{

        log.Printf("error %v", err)

        return

    }

    defer cancel.Cancel()

    for state := range watchState{

        log.Printf.("state is %v", state)

    }

}

恐慌痕迹

panic: runtime error: invalid memory address or nil pointer dereference

[signal 0xb code=0x1 addr=0x0 pc=0x488788]

    goroutine 1 [running]:

    launchpad.net/go-dbus/v1.(*ObjectProxy).WatchSignal(0x0, 0x616cd0, 0x1e, 0x5f0af0, 0xc, 0x7f9733d0e478, 0x0, 0x0)

        /root/go/src/launchpad.net/go-dbus/v1/dbus.go:97 +0x198

    launchpad.net/ubuntu-push/bus.(*endpoint).WatchSignal(0xc20803e0c0, 0x5f0af0, 0xc, 0xc20800a0e0, 0xc20802a530, 0x0, 0x0, 0x0, 0x0)

        /root/go/src/launchpad.net/ubuntu-push/bus/endpoint.go:133 +0x91

    launchpad.net/ubuntu-push/bus/networkmanager.(*networkManager).WatchState(0xc20800a0c0, 0x5bce80, 0x0, 0x0, 0x0, 0x0)

        /root/go/src/launchpad.net/ubuntu-push/bus/networkmanager/networkmanager.go:108 +0x1cf

    main.main()

        /root/go/src/github.com/vinkoo/net/main.go:16 +0x1f9

    goroutine 2 [runnable]:

    runtime.forcegchelper()

        /usr/local/go/src/runtime/proc.go:90

    runtime.goexit()

        /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1

    goroutine 3 [runnable]:

    runtime.bgsweep()

        /usr/local/go/src/runtime/mgc0.go:82

    runtime.goexit()

        /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1