how to append nil to dynamic type slice by reflect.Append

Code below will raise a runtime error when append reflect.Value of nil:

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var list []interface{}
    v := reflect.ValueOf(list)
    v = reflect.Append(v, reflect.ValueOf(1))   // [1]
    v = reflect.Append(v, reflect.ValueOf("1")) // [1, 1]
    v = reflect.Append(v, reflect.ValueOf(nil)) // runtime error
    fmt.Println(v)
}

So

• why there is a runtime error?
• how can I use reflect.Append to add a nil to interface{} slice?