Why Go does not panic when trying to read from a nil map?

Question

Here is the code, I expect it will panic when visiting mp["12"], but it works fine there

// You can edit this code!
// Click here and start typing.
package main

import "log"

func main() {
    var mp map[string]int = nil
    log.Println(mp["12"], "12") // works fine
    if mp == nil {
        panic("map is nil") // panic here
    }
}

Answer 1

You can read from a nil map, but cannot write to it. The language spec says:

A nil map is equivalent to an empty map except that no elements may be added.