Default validation message is not showing for newsletter

For showing In normally if we didn’t enter anything in email field it will shows an error message but if message is not getting we need to customize and created a new extension for that and check

Configuration :

{
    "type": "object",
    "subtab": {
        "id": "Newsletter",
        "group": "extensions",
        "title": "Newsletter"
    },
    "properties": {
        "newsletter.FirstName": {
            "group": "extensions",
            "subtab": "Newsletter",
            "type": "string",
            "title": "Newsletter First Name",
            "description": "Config description example",
            "default": "First Name"
        },
        "newsletter.LastName": {
            "group": "extensions",
            "subtab": "Newsletter",
            "type": "string",
            "title": "Newsletter Last Name",
            "description": "Config description example",
            "default": "Last Name"
        },
        "newsletter.CompanyName": {
            "group": "extensions",
            "subtab": "Newsletter",
            "type": "string",
            "title": "Newsletter Company Name",
            "description": "Config description example",
            "default": "Company Name"
        }
    }
}

Suitescript : 

// Define a module 'JJ.newsLetter.newsLetter' and declare its dependencies
define('JJ.NewsLetter.NewsLetter', [
    'Newsletter.Model', 
    'SC.Models.Init',
    'underscore', 
    'Utils', 
    'Configuration',
    'SC.Model'
]
    , function (
        NewsletterModel, 
        ModelsInit, 
        _, 
        Utils, 
        Configuration, 
        SCModel
) {
    'use strict';
    _.extend(NewsletterModel, {
        //Using 'createSubscription' method to create a new reacord
        createSubscription: function createSubscription(email) {
            try {
                // Create a new NetSuite 'lead' record
                var record = nlapiCreateRecord('lead');
                // Set field values of the 'lead' record
                record.setFieldValue('entityid', email);
                record.setFieldValue('firstname', Configuration.get('newsletter.FirstName'));
                record.setFieldValue('lastname', Configuration.get('newsletter.LastName'));
                record.setFieldValue('email', email);
                record.setFieldValue('subsidiary', ModelsInit.session.getShopperSubsidiary());
                record.setFieldValue('companyname', Configuration.get('newsletter.CompanyName'));
                // Submit the 'lead' record to NetSuite
                nlapiSubmitRecord(record, true, true);
                return this.subscriptionDone;
            }
            catch (e) {
                console.log("err@createSubscription", e);
            }
        },
    })
});