[Go] Default value for non-existing key in map.

package main

import (
    "log"
)

func main() {
    m := make(map[string]string)

    m["Go"] = "Beego"
    m["Python"] = "Django"
    m["Ruby"] = "Rails"
    m["PHP"] = "Laravel"

    // No such key/value pair.
    if !(m["Java"] == "") {
        log.Fatal("Wrong value")
    }
}