Perhaps this time it is "Hindsight", but next time it could be "Lesson Learned", "Experience", "Defensive Programming", or, Monastary forbid, a "Good Engineering Practice".

This incident has added a rather large stone on the scale which was already precariously close to tipping in favor of switching to the use of Data::Dumper over my rather obsolete and unrobust homespun debug module from longer ago than I'd care to admit.

Thanks for the analysis and summary. Thanks to the OP for posting -- and clarifying -- the problem.