If the deployment scanner element is removed from the configuration of the standalone server a NullPointerException is logged which is unclear and difficult to find as the stack does not show any hint.

Config:

{xml}
<subsystem xmlns="urn:jboss:domain:deployment-scanner:2.0">
<!-- deployment-scanner path="deployments" relative-to="jboss.server.base.dir" scan-interval="5000" runtime-failure-causes-rollback="${jboss.deployment.scanner.rollback.on.failure:false}"/ -->
</subsystem>{xml}

Log message:
ERROR [org.jboss.as.controller.management-operation] (ServerService Thread Pool – 34) WFLYCTL0403: Unexpected failure during execution of the following operation(s): []: java.lang.NullPointerException
at org.jboss.as.controller.AbstractOperationContext$Step.access$300(AbstractOperationContext.java:1185)
at org.jboss.as.controller.AbstractOperationContext.executeResultHandlerPhase(AbstractOperationContext.java:767)
at org.jboss.as.controller.AbstractOperationContext.executeDoneStage(AbstractOperationContext.java:753)
at org.jboss.as.controller.AbstractOperationContext.processStages(AbstractOperationContext.java:680)
at org.jboss.as.controller.AbstractOperationContext.executeOperation(AbstractOperationContext.java:370)
at org.jboss.as.controller.ParallelBootOperationStepHandler$ParallelBootTask.run(ParallelBootOperationStepHandler.java:359)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
at org.jboss.threads.JBossThread.run(JBossThread.java:320)