On publish I would like to set a value to a numeric textbox on my documenttype Product  to 0 only if it is empty.

I did this, but it does no good.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using umbraco.BusinessLogic;
using umbraco.cms.businesslogic;
using umbraco.cms.businesslogic.web;
using umbraco;

namespace AutoSetPrice
{
    public class AutoSetPriceHandler
    {
        public AutoSetPriceHandler()
        {
            Document.BeforePublish += new Document.PublishEventHandler(Document_BeforePublish);
        }

        void Document_BeforePublish(Document sender, PublishEventArgs e)
        {
            if (sender.ContentType.Alias == "Product")
            {
                if (sender.getProperty("price").Value == null || sender.getProperty("price").Value.ToString() == "")
                {
                    sender.getProperty("price").Value = 0;
                    umbraco.library.UpdateDocumentCache(sender.Id);
                }
            }
        }
    }
}