请教关于redigo的问题

redigo http://github.com/garyburd/redigo/redis

go redis client的一个库

如下代码：

package main
import(
    "fmt"
    "github.com/garyburd/redigo/redis"
)

func main(){
    c, err := redis.Dial("tcp", ":6379")
    c.Do("SET", "foo", "bar")
    v, err := c.Do("GET", "foo")
    if err != nil{
        fmt.Println(err)
    } else {
        fmt.Println(v)
    }
}

运行下，出错：

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x28 pc=0x2174]

goroutine 1 [running]:
main.main()
    /Users/jay/mygo/src/golearn/rd2.go:9 +0x174

goroutine 2 [syscall]:
exit status 2

why? thanks