Back to Top jQuery - Uncaught Typeerror: Cannot read Property 'top' of Undefined

Question

I have the script to get back to TOPO. On the home page of the site, it works perfectly, however, on the internal pages it does not go up and presents the following error:

Uncaught Typeerror: Cannot read Property 'top' of Undefined

jQuery

$(document).ready(function () {
  'use strict';
  /* ========================================================================
     Fullscreen burger menu
   ========================================================================== */
  $(".menu-trigger, .mobilenav").click(function () {
    $(".mobilenav").fadeToggle(500);
  });
  $(".menu-trigger, .mobilenav").click(function () {
    $(".top-menu").toggleClass("top-animate");
    $(".mid-menu").toggleClass("mid-animate");
    $(".bottom-menu").toggleClass("bottom-animate");
  });

  /* ========================================================================
     On click menu item animate to the section
   ========================================================================== */
  $(".mobilenav li, .back-to-top").on('click', function() {
    var target = $(this).data('rel');
    var $target = $(target);
    $('html, body').stop().animate({
        'scrollTop': $target.offset().top
    }, 900, 'swing');
  });

Error forwards the following line:

'scrollTop': $target.offset().top

Where I’d be wrong?