I'm having trouble setting up my Form Schedule in Zoho Creator.

Situation

I add assignments to my employees trough the system. The employees have to make an appointment with our customer. The appointment date is then saved in the assignment row (called Afspraak, Dutch for appointment), to keep track of 'open' assignments. Afspraak is a datetime field.

The emloyees are expected to to this in 24 hours after the creation date of the assignment, but sometimes it takes up to 48 hours or even more. In these cases, the employees should be remembered to add the appointment date to the system.

Therefore I setup two Form Schedules: 24 and 48 hours after creation date. Both with filter " Afspraak is null". So it states:

1. Execute on 1 days after of Opdracht_toevoegen[(Afspraak is null)].Added_Time  

Problem

The schedule runs always: to the entries with or without assignment. This isn't what I expected, since " Afspraak is null" isn't true in my eyes, when an ' Afspraak' is entered..

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Does anyone know how to solve this issue?

Thanks in advance!