Error "Cannot set Property 'checked' of Undefined"

Question

In the store here is giving an error in the prototype:

Uncaught TypeError: Cannot set property 'checked' of undefined
at klass.<anonymous> (product.js:128)
at prototype.js:391
at prototype.js:825
at klass._each (prototype.js:1237)
at klass.each (prototype.js:824)
at klass.updateImages (product.js:125)
at klass.initialize (product.js:55)
at klass (prototype.js:101)
at (index):1205

And in the error code, this appears:

var $break = {};
var Enumerable = (function() {
      function each(iterator, context) {
        var index = 0;
        try {
          this._each(function(value) {
            iterator.call(context, value, index++);
          });
        } catch (e) {
          if (e != $break) throw e;
        }
        return this;
      }