Looks like you haven’t copied the code exactly as was shown in this post:
I also get a fatal error using that code when a blank date time field is found. (Like on a new record). An easy workaround would be to use a model condition to set the date time field to “TODAY” which pulls in the current time as well as the current date. Otherwize you will have to add some code to handle the scenario where “value” is blank.
