The NullPointerException happens when a logger.debug(exception) is made with an exception with a 'null' message. This bug only manifests itself when -Dcdk.debugging=true is uses (i.e. debugging is turned on).
This patch splits out tests which should be run with and without debugging turned out into an "abstract" test class, with two extensions, each instantiating a LoggingTool in an appropriate way (with or without debugging on).
The second patch contains a unit test for the NPE, and the third patch a fix.