Using Fast Data Masker (FDM) to mask a very large number of rows. The requirement that must be fulfilled is the need to be able to restart the job if there is an error due. It is known that the data is not clean. When the restartability column's value is null, a Null Pointer Exception (NPE) occurs after setting the restartability column's value to null.
After researching this issue, the behavior was narrowed down to if a column's value is null, even if the Keep Null's checkbox is checked, AND if restartability is enabled, there is a NPE thrown in the console each time.
If the restartability column is removed and its options before masking, no problem occurs.