json.NewDecoder(r.Body).Decode(&admin) returns empty struct

Question

I know there are a lots of people that has run into the same issue but still here I am. I'm pretty sure my code is correct and still the resulting struct is empty. Function :

func PostAdminHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-type", "application/json")
    var admin admin.Admin

    json.NewDecoder(r.Body).Decode(&admin)
    fmt.Println(admin)
    _, err := PostAdmin(admin)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
    }
}

Console print :

{     ObjectID("000000000000000000000000")}

Structure :

package entity

import "go.mongodb.org/mongo-driver/bson/primitive"

type Admin struct {
    FirstName string
    LastName  string
    Email     string
    Password  string
    Role      string
    Campus    primitive.ObjectID
}

Route :

    adminRoute.HandleFunc("/admin", admin.PostAdminHandler).Methods("POST")

Json data I'm sending through Insomnia :

{
    "FirstName": "Jeanne",
    "LastName": "Darc",
    "Email": "[email protected]",
    "Password": "JeanneDarc2022",
    "Role": "admin",
    "Campus": "60d5a25ff4d722d3b77d1929",
}

Error i'm getting from decoder :

invalid character '}' looking for beginning of object key string

Answer 1

This RFC:

https://datatracker.ietf.org/doc/html/rfc7159

specifies the JSON object format as:

An object structure is represented as a pair of curly brackets
surrounding zero or more name/value pairs (or members). A name is a
string. A single colon comes after each name, separating the name
from the value. A single comma separates a value from a following
name. The names within an object SHOULD be unique.

object = begin-object [ member *( value-separator member ) ]
               end-object

member = string name-separator value

So, no trailing commas.

Remove the last comma in the input.