gob：类型未为接口注册：[] interface {}

Question

I am trying to copy a map to another map so i used gob in order to do this. But when i unmarshal a json to map[string]interface{} and then try to copy it to another map i get an error in the encoding part.

This is the code:

    package main

import (
    "encoding/gob"
    "bytes"
    "fmt"
    "encoding/json"
)

func CopyMapToAnotherMap(req map[string]interface{}) (cpy map[string]interface{}, err error) {
    var mod bytes.Buffer
    gob.Register(map[string]interface{}{})
    enc := gob.NewEncoder(&mod)
    dec := gob.NewDecoder(&mod)

    err = enc.Encode(req)
    if err != nil {
        fmt.Println("Unable to encode map", err)
        return nil, err
    }

    err = dec.Decode(&cpy)
    if err != nil {
        fmt.Println("Unable to decode map", err)
        return nil, err
    }

    return cpy, nil
}

func main() {
    my := `{"data":[{"aa":1},{"bb":2}]}`
    var m map[string]interface{}

    err := json.Unmarshal([]byte(my), &m)
    if err !=  nil {
        fmt.Println(err)
    }
    CopyMapToAnotherMap(m)
}

and i am getting an error : gob: type not registered for interface: []interface {}

How can this be avoided?