It is by design that if a date is null, it writes the current date to the database. You can override this behavior though.
If you select operator’s properties you would see a check box called “Display null values” like below.
When it is checked it is going to generate another array of values named “NullFieldFlags”.
From the PAM documentation
NullFieldFlags
An array of ValueMaps. The fields of each ValueMap correspond to the fields in rows. The value of each field is either true. The corresponding value in rows is null, or false otherwise. This output only displays if Display null values is selected.
In Simple words:
It is an array of valuemap filled with Booleans. A value of true means that corresponding value in the results no matter what is in the results, the value is null in the database. Like shown below that the date has the Boolean true while name has false. That means date field is null is the database.