goweb学习，学习到表单处理表单的输入的时胡，和书上写的一样，但是运行却报错

package main



import (

    "fmt"

    "html/template"

    "log"

    "net/http"

    "strings"

)



func sayHelloName(w http.ResponseWriter, r *http.Request){

    r.ParseForm()

    fmt.Println(r.Form)

    fmt.Println("path", r.URL.Path)

    fmt.Println("scheme", r.URL.Scheme)

    fmt.Println(r.Form["url_long"])

    for k,v := range r.Form {

        fmt.Println("key: ", k)

        fmt.Println("val: ", strings.Join(v, ""))

    }

    fmt.Fprintf(w, "hello astaxie!")

}



func login(w http.ResponseWriter, r *http.Request) {

    fmt.Println("method:", r.Method) //获取请求的方法

    if r.Method == "GET" {

        t, _ := template.ParseFiles("login.gtpl")

        t.Execute(w, nil)

    } else {

        //请求的是登陆数据，那么执行登陆的逻辑判断

        fmt.Println("username:", r.Form["username"])

        fmt.Println("password:", r.Form["password"])

    }

}



func main() {

    http.HandleFunc("/", sayHelloName)

    http.HandleFunc("/login", login)

    err := http.ListenAndServe(":9090", nil)

    if err != nil{

        log.Fatal("ListenAddServer: ", err)

    }

}

method: GET

2019/10/22 15:19:22 http: panic serving 127.0.0.1:64117: runtime error: invalid memory address or nil pointer dereference

goroutine 6 [running]:

net/http.(*conn).serve.func1(0xc0000650e0)

    D:/golang/src/net/http/server.go:1767 +0x140

panic(0x780880, 0xabfe80)

    D:/golang/src/runtime/panic.go:679 +0x1c0

html/template.(*Template).escape(0x0, 0x0, 0x0)

    D:/golang/src/html/template/template.go:95 +0x49

html/template.(*Template).Execute(0x0, 0x869920, 0xc000102000, 0x0, 0x0, 0x869a60, 0xc0000ca150)

    D:/golang/src/html/template/template.go:119 +0x36

main.login(0x86f5e0, 0xc000102000, 0xc0000ee000)

    E:/go_code/src/demo1/main/main.go:28 +0x34d

net/http.HandlerFunc.ServeHTTP(0x807338, 0x86f5e0, 0xc000102000, 0xc0000ee000)

    D:/golang/src/net/http/server.go:2007 +0x4b

net/http.(*ServeMux).ServeHTTP(0xacfa00, 0x86f5e0, 0xc000102000, 0xc0000ee000)

    D:/golang/src/net/http/server.go:2387 +0x1c4

net/http.serverHandler.ServeHTTP(0xc0000c4000, 0x86f5e0, 0xc000102000, 0xc0000ee000)

    D:/golang/src/net/http/server.go:2802 +0xab

net/http.(*conn).serve(0xc0000650e0, 0x86fba0, 0xc0000cc000)

    D:/golang/src/net/http/server.go:1890 +0x87c

created by net/http.(*Server).Serve

    D:/golang/src/net/http/server.go:2927 +0x395