Tests failing with Pantools.logger

In ProteomeLayer.java, replacing System print with Pantools.logger statements cause tests to fail. This happen only in methods that are being tested, e.g. in public ArrayList<String> check_which_rn_to_use(boolean print, String input_values) if I replace

System.out.println("Numbers are only allowed to be seperated by a comma");

with

Pantools.logger.error("Numbers are only allowed to be seperated by a comma");

It throws the following test error:

[ERROR] Tests run: 32, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 14.931 s <<< FAILURE! - in nl.wur.bif.pantools.pangenome.ProteomeLayerTest$Neo4jTests

[ERROR] nl.wur.bif.pantools.pangenome.ProteomeLayerTest.checkWhichRnToUseTest  Time elapsed: 0.016 s  <<< FAILURE!

org.opentest4j.MultipleFailuresError: 
Multiple Failures (1 failure)
	java.lang.NullPointerException: <no message>
	at nl.wur.bif.pantools.pangenome.ProteomeLayerTest.checkWhichRnToUseTest(ProteomeLayerTest.java:41)