golang值为nil的channel

golang中在一个值为 nil 的 channel 上发送和接收数据将永久阻塞

package main

import (
	"fmt"
	"time"
)

func main() {
	ch := make(chan int)
	for i := 0; i < 3; i++ {
		go func(idx int) {
			ch <- idx
		}(i)
	}
	fmt.Println(<-ch)	
	close(ch)			
	time.Sleep(2 * time.Second)	
}

运行出错：fatal error: all goroutines are asleep - deadlock!