The following null-checks should be added (as uncovered in
1. BaseContentService.getResource() doesn't nullcheck before calling unlock() (many other places call unlock() without nullchecks, too).
2. BaseContentService.unlock() doesn't nullcheck the ID before calling convertLockIfDropbox().
3. BaseContentService.convertLockIfDropbox(), doesn't nullcheck before string comparison.
4. BaseContentService.isAttachmentResource() does not nullcheck the ID before string comparison.