Fix main Spotbugs issues #1849
Description
After the introduction of Spotbugs in the 2.x build, some issues were discovered that need addressing.
Spotbugs ranks the issues from 1 to 20 (cf. documentation), with ranks 1-4 classified as scariest, 5-9 as scary, 10-14 as troubling and 15-20 as simple bugs.
We need to address ranks 1-14 by either correcting the code or marking them as false positives.