Error when running Supply Plan with External Data

Summary

After loading my data from external source, I created a Plan. When I run it, I'm getting an error in the Demand Snapshot process

Content

There is an error being generated out of the method generateGregorianCalendarDates.  Due to this error, I cannot do anything with the plan.  The full text of the log for this process is shown below.  It's not much help in understanding what the root cause is.  I've not found anything in My Oracle Support that seems to address this.  Open to any or all suggestions from the experts out there.  Hoping I can avoid opening an SR for this.