Second line is a potential NPE if the MRR tree has changed since 'element' was found:

final ImmutableManagementResourceRegistration childRegistration = registry.getSubModel(PathAddress.pathAddress(element));
final AliasEntry aliasEntry = childRegistration.getAliasEntry();

Failed here:

http://brontes.lab.eng.brq.redhat.com/viewLog.html?buildId=92710&buildTypeId=WildFlyCore_PullRequest_WildFlyCoreFullIntegration

======= Failed test run #1 ==========
org.jboss.as.test.integration.management.util.MgmtOperationException: Management operation failed.
at org.jboss.as.test.integration.domain.management.util.DomainTestUtils.executeForResult(DomainTestUtils.java:160)
at org.jboss.as.test.integration.domain.mixed.DomainHostExcludesTest.readChildrenNames(DomainHostExcludesTest.java:302)
at org.jboss.as.test.integration.domain.mixed.DomainHostExcludesTest.stopSlave(DomainHostExcludesTest.java:111)
at org.jboss.as.test.integration.domain.mixed.DomainHostExcludesTest.setup(DomainHostExcludesTest.java:93)
at org.jboss.as.test.integration.domain.mixed.eap630.DomainHostExcludes630TestCase.beforeClass(DomainHostExcludes630TestCase.java:40)
------- Stdout: -------
...
&amp#27;[0m[Host Controller] &amp#27;[0m&amp#27;[0m22:06:43,569 INFO [org.jboss.as.domain.controller] (management task-5) WFLYHC0026: Unregistered remote slave host "slave"&amp#27;[0m
[Host Controller] &amp#27;[0m&amp#27;[31m22:06:43,569 ERROR [org.jboss.as.controller.management-operation] (management-handler-thread - 3) WFLYCTL0013: Operation ("read-children-names") failed - address: ([]): java.lang.NullPointerException&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.operations.global.GlobalOperationHandlers.getChildAddresses(GlobalOperationHandlers.java:960)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.operations.global.ReadChildrenNamesHandler.execute(ReadChildrenNamesHandler.java:78)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:890)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.AbstractOperationContext.processStages(AbstractOperationContext.java:659)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.AbstractOperationContext.executeOperation(AbstractOperationContext.java:370)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.OperationContextImpl.executeOperation(OperationContextImpl.java:1344)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.ModelControllerImpl.internalExecute(ModelControllerImpl.java:392)&amp#27;[0m
[Host Controller] &amp#27;[31m at org.jboss.as.controller.ModelControllerImpl.execute(ModelControllerImpl.java:217)&amp#27;[0m
[Host Controller] &amp#27;
...

The test stops host slave and then starts reading children names of type 'host' to see when 'slave' is gone. The registration disappears in the middle of the getChildAddresses logic resulting in NPE.