Event based remote active replication does not work in HA set up, with NullPointerException

How to reproduce:

• Set up two Artifactory instance (A & B), and the instance A is with HA setup, with two backends.
• Create local repo docker-v2-hub-local in instance A, and remote repo docker-v2-hub-remote in instance B, which points to docker-v2-hub-local in instance A.
• Set up active remote replication for docker-v2-hub-remote, and enable event based replication.
  It is supposed that the request of "/api/replications/channells/establishChannel" is sent to the master of instance A.
• Deploy an artifact to docker-v2-hub-local, through the master of instance A. We can observe the artifacts appears in docker-v2-hub-remote right away.
• Deploy another artifact to docker-v2-hub-local, but through the slave of instance A. Now we can observe below exception in the slave, and the replication does not happen:

2018-09-27 07:30:23,241 [http-nio-8082-exec-9] [INFO ] (o.j.r.d.v.r.h.DockerV2LocalRepoHandler:258) - Deploying docker manifest for repo 'proj_armserv/arm_testi/busybox' and tag 'latest' into repo 'docker-v2-hub-local'
2018-09-27 07:30:23,474 [art-exec-5] [ERROR] (o.a.a.h.p.HaPropagationServiceImpl:382) - Error waiting for propagation event: java.lang.NullPointerException
java.util.concurrent.ExecutionException: java.lang.NullPointerException
        at java.util.concurrent.FutureTask.report(FutureTask.java:122)
        at java.util.concurrent.FutureTask.get(FutureTask.java:206)
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.getResponse(HaPropagationServiceImpl.java:378)
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
        at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
        at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.propagateInternal(HaPropagationServiceImpl.java:372)
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.multiTryPropagation(HaPropagationServiceImpl.java:301)
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.propagate(HaPropagationServiceImpl.java:286)
        at sun.reflect.GeneratedMethodAccessor466.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:201)
        at com.sun.proxy.$Proxy253.propagate(Unknown Source)
        at org.artifactory.addon.ha.HaAddonImpl.propagateAndGetContentList(HaAddonImpl.java:725)
        at org.artifactory.addon.ha.HaAddonImpl.propagateReplicationEvents(HaAddonImpl.java:683)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
        at org.artifactory.schedule.aop.TraceableMethodInvocation.proceed(TraceableMethodInvocation.java:58)
        at org.artifactory.schedule.aop.AsyncAdvice.doInvoke(AsyncAdvice.java:333)
        at org.artifactory.schedule.aop.AsyncAdvice.lambda$submit$2(AsyncAdvice.java:285)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at org.artifactory.concurrent.ArtifactoryRunnable.run(ArtifactoryRunnable.java:30)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

Caused by: java.lang.NullPointerException: null
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.getServerName(HaPropagationServiceImpl.java:515)
        at org.artifactory.addon.ha.propagate.HaPropagationServiceImpl.lambda$getServerResponse$2(HaPropagationServiceImpl.java:396)
        ... 5 common frames omitted

2018-09-27 07:30:23,476 [art-exec-5] [ERROR] (o.a.a.h.p.HaPropagationServiceImpl:319) - Failed to propogate - sleeping...

The same error also happens, if the establishChannel request happens to be sent to the slave of instance A, then the artifact is deployed through the master.