From Xojo Documentation
Return something that indicates the job to process. This information is supplied as the parameter to JobRun. You should avoid passing around large chunks of data as that will not be memory efficient. If you have large data (pictures, data, databases, etc.) then pass along information on how to get the data using other means such as file access or connecting to the database and fetching what is needed.
Returning an empty string indicates that there are no more jobs to process and that the worker should quit.
The encoding of the jobData that you return is not preserved. Apply the encoding in JobRun as necessary.