If there is an error in the expression passed to JaninoEventEvaluator, then
the JaninoEE will throw an excpetion, sometimes an NPE to higher levels.
Loggers do not seem to catch the NPE, nor does EvaluatorFilter.

Here is a stack trace:

Exception in thread "main" java.lang.NullPointerException
at ch.qos.logback.core.boolex.JaninoEventEvaluatorBase.evaluate(JaninoEventEvaluatorBase.java:58)
at ch.qos.logback.core.filter.EvaluatorFilter.decide(EvaluatorFilter.java:48)
at ch.qos.logback.core.spi.FilterAttachableImpl.getFilterChainDecision(FilterAttachableImpl.java:68)
at ch.qos.logback.core.AppenderBase.getFilterChainDecision(AppenderBase.java:115)
at ch.qos.logback.core.AppenderBase.doAppend(AppenderBase.java:65)
at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:51)
at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:286)
at ch.qos.logback.classic.Logger.callAppenders(Logger.java:270)
at ch.qos.logback.classic.Logger.filterAndLog(Logger.java:375)
at ch.qos.logback.classic.Logger.debug(Logger.java:398)
at chapter5.GoMDC.main(GoMDC.java:28)

The expresison is:

<Expression>message.conts("I know me 1")</Expression>