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