When the output of a cleanse function is a null value, the
cleanse
API returns no information about that field.
It is assumed that the function is not changing that field. If the goal is for the cleanse function to override a value with NULL the options depend on the data type, then following is required:
String - The function can be changed to return an empty string.
Date or numeric - A user exit must be implemented to modify the data. The beforeEverything() or beforeSave() methods of the Save handler can be used.