title: Hidden input are not sending something via Ajax
body: <p>Sometime i am getting error about missing post data from Ajax, this isn't happen every-time and i cant understand why i am getting error message like this in my controller</p>
  <blockquote>
  <p>PHP Notice:  Undefined index: product_id</p>
  </blockquote>
  <p>Template</p>
  <pre><code>&lt;ul class=&quot;block-price&quot;&gt;
      &lt;li&lt;?php if (!$stock): ?&gt; style=&quot;display:none&quot; &lt;?php endif; ?&gt;&gt;
          &lt;i onclick=&quot;priceUpdate('plus');&quot;  class=&quot;fa fa-minus price-minus&quot; aria-hidden&gt;&lt;/i&gt;
          &lt;input type=&quot;text&quot; name=&quot;quantity&quot; value=&quot;&lt;?php echo $minimum; ?&gt;&quot; size=&quot;2&quot; id=&quot;input-quantity&quot; class=&quot;form-control&quot; /&gt;
          &lt;i onclick=&quot;priceUpdate('minus');&quot;  class=&quot;fa fa-plus price-plus&quot; aria-hidden&gt;&lt;/i&gt;
          &lt;input type=&quot;hidden&quot; name=&quot;product_id&quot; value=&quot;&lt;?php echo $product_id; ?&gt;&quot; /&gt;
      &lt;/li&gt;
  &lt;/ul&gt;
  
     
  </code></pre>
  <p>jQuery</p>
  <pre><code>function priceUpdate(type) {
      var i = parseInt($('#input-quantity').val());
  
      if(type == 'plus'){
          f = Number(i + 1).toString();
      }else{
          f = Number(i - 1).toString();
      }
  
      $('input[name=&quot;quantity&quot;]').val(''+f+'').trigger('change')
  }
  $('#product').on('input change', 'input, select', function() {
      $.ajax({
          url: 'index.php?route=priceUpdate',
          type: 'post',
          data: $('#product input[type=\'hidden\'], #product input[type=\'checkbox\']:checked, #product select'),
          dataType: 'json',
          success: function(json) {
  
          }
      });
  });
  </code></pre>
  <p>Controller</p>
  <pre><code>public function priceUpdate(){
    $data = [
     'cart_id'        =&gt; false,
     'product_id'     =&gt; $this-&gt;request-&gt;post['product_id'], (error message is this lane)
     'quantity'       =&gt; $quantity
    ];
  }
  </code></pre>