title: How to submit multiple products to PayPal, with some having 0 quantity
body: <p>I'm trying to set up a simple, one-page "buy now" form with multiple product listings and a text input box allowing users to specify how much they would like of each product OR specifying '0' to not add the product to the cart. Of course, if someone just has 0 for a quantity, PayPal returns "You have entered an invalid quantity value. A quantity value must be an integer greater than or equal to one." Is there an easy work-around for getting PayPal to ignore products submitted that have a quantity of "0"? My form essentially it looks like this (fields like total_item_* are for the jquery calculation script):</p>
  
  <pre><code>&lt;form action="https://www.paypal.com/cgi-bin/webscr" method="post" id="frmCreateCheckboxRange"&gt;
  &lt;input type="hidden" name="cmd" value="_cart"&gt;
  &lt;input type="hidden" name="upload" value="1"&gt;
  &lt;input type="hidden" name="business" value="youremail@mail.com"&gt;
  &lt;input type="hidden" name="currency_code" value="US"&gt;
  
  &lt;fieldset&gt;
  &lt;table width="500"&gt;
  
  &lt;!-- Product 1 --&gt;
  &lt;tr&gt;
  &lt;td align="center"&gt;
  &lt;input type="text" name="quantity_1" id="qty_item_1" value="0" size="2" /&gt;
  &lt;input type="hidden" name="item_name_1" value="Non-Driver Event Pit Passes (6/ 29 - 7/ 2)" /&gt;
  &lt;input type="hidden" name="amount_1" value="30.00" /&gt;
  &lt;/td&gt;
  &lt;td&gt;Non-Driver Event Pit Passes (6/ 29 - 7/ 2)&lt;/a&gt;&lt;/td&gt;
  &lt;td align="center" id="price_item_1"&gt;$30.00&lt;/td&gt;
  &lt;td align="center" id="total_item_1"&gt;$0.00&lt;/td&gt;
  &lt;/tr&gt;
  
  &lt;!-- Product 2 --&gt;
  &lt;tr&gt;
  &lt;td align="center"&gt;
  &lt;input type="text" name="quantity_2" id="qty_item_2" value="0" size="2" /&gt;
  &lt;input type="hidden" name="item_name_2" value="Non-Driver Single Day Pit Passes (Fri. 6/29)" /&gt;
  &lt;input type="hidden" name="amount_2" value="15.00" /&gt;
  &lt;/td&gt;
  &lt;td&gt;Non-Driver Single Day Pit Passes (Fri. 6/29)&lt;/td&gt;
  &lt;td align="center" id="price_item_2"&gt;$15.00&lt;/td&gt;
  &lt;td align="center" id="total_item_2"&gt;$0.00&lt;/td&gt;
  &lt;/tr&gt;
  &lt;/table&gt;
  
  &lt;input type="image" src="http://www.paypal.com/en_US/i/btn/x-click-but01.gif" name="submit"&gt;
  &lt;/fieldset&gt;
  &lt;/form&gt;
  </code></pre>