Error executing if/while condition

Error executing if/while condition

Hi. I have the following code in my Guest Tracker application, which worked fine in the past. Now every time I add a new guest the new record gets updated but I get an error in the 'on success' function. Is this a Zoho bug? I haven't changed the logic.

I've shared my application with support.

Code is below:

on success
{
input.Modified_By = zoho.loginuser;
input.Modified_Date1 = zoho.currenttime;
if ((input.Latest_Contact_Date is null) || (input.First_Visit > input.Latest_Contact_Date))
{
input.Latest_Contact_Date = input.First_Visit;
}
if ((input.Latest_Contact_Date is null) || (input.Second_Visit > input.Latest_Contact_Date))
{
input.Latest_Contact_Date = input.Second_Visit;
}
if ((input.Latest_Contact_Date is null) || (input.Third_Visit > input.Latest_Contact_Date))
{
input.Latest_Contact_Date = input.Third_Visit;
}
}