每當網絡狀態發生變化時，我都需要觀察網絡變化并設置一些路由規則（例如，如果接口重新啟動，我需要再次設置 ip 路由表 b/c src 是動態的，因此我無法對其進行硬編碼）。為了實現這一點，我正在嘗試使用networkmanager包，但 WatchState 會出現恐慌。知道為什么嗎？package mainimport(    "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)    }}恐慌痕跡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