Mongoose data saving without _id

I am using mongoose with node.js application. I don't want _id field in record. I am using this code to save my record without _id field. But it is giving error

document must have an _id before saving

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var PlayerSchema = new Schema({
    player_id :  { type: Number },
    player_name : { type: String },
    player_age  : { type: Number },
    player_country : { type: String }
}
, { _id: false }
);

var Player =  mongoose.model('Player', PlayerSchema );

        var athlete = new Player();
        athlete.player_id = 1;
        athlete.player_name = "Vicks";
        athlete.player_age  = 20;
        athlete.player_country = "UK";

        athlete.save(function(err) {
            if (err){
                console.log("Error saving in PlayerSchema"+ err);
            }
        });

I am using mongoose version 3.8.14