golang反射的零值如何判断

package main

import (

    "fmt"

    "reflect"

)

func main() {

    var p1 *string = nil

    var v interface{} = p1

    val := reflect.Indirect(reflect.ValueOf(v))

    if v == nil {

        fmt.Printf("NULL")

    } else {

        if val.CanInterface() {

            fmt.Printf("if is %v\n", val.Interface())

        }

    }

}

这个程序的输出是：

···

panic: reflect: call of reflect.Value.CanInterface on zero Value

goroutine 1 [running]:

panic(0xd65a0, 0xc82005e000)

    /usr/local/go/src/runtime/panic.go:464 +0x3e6

reflect.Value.CanInterface(0x0, 0x0, 0x0, 0x0)

    /usr/local/go/src/reflect/value.go:897 +0x62

···

怎么了？为什么v == nil是false？