Hi, am attaching to the BeforePublsh to set a property value of a document type. It works fine, but now I want to check if the user has entered a value before attempting to set it programatically. Here' what I have:

//Always LOG
Log.Add(LogTypes.Custom, sender.Id, "Attempting to set the expiration date of CLASSIFIED AD: " + sender.Text);

if (sender.ContentType.Alias == "ClassifiedAd")
{
    DateTime dt = DateTime.Now;
    if (sender.getProperty("adExpirationDate").Value == null) sender.getProperty("adExpirationDate").Value = dt.AddDays(21);
 }

 Log.Add(LogTypes.Custom, sender.Id, "Expiration set successfully: " + sender.Text);

When the date has been left blank, the Value is not null. How can I check if it is empty?

Thanks,
Nik