PAHMA-738: Allow event listener to 'null out' computedCrate value in Cataloging / CollectionObject if that value is blank / null in most recent related Movement record.
PAHMA-738: Correct one comment.
PAHMA-738: Reworked logic of non-blank tests.
Merge pull request #6 from aronr/PAHMA-738

PAHMA-738: Allow computedCrate in Cataloging to be 'nulled out' if crate value in most recent Movement is blank.