Avoid NPE when reading Artemis cluster status while Artemis broker isn't fully started

11:00:36,718 ERROR [org.jboss.as.controller.management-operation] (management-handler-thread - 1) WFLYCTL0013: Operation ("read-attribute") failed - address: ([
("subsystem" => "messaging-activemq"),
("server" => "default"),
("ha-policy" => "replication-slave")
]): java.lang.NullPointerException
at org.wildfly.extension.messaging-activemq//org.wildfly.extension.messaging.activemq.ha.HAPolicySynchronizationStatusReadHandler.executeRuntimeStep(HAPolicySynchronizationStatusReadHandler.java:61)
at org.jboss.as.controller@10.0.0.Final//org.jboss.as.controller.AbstractRuntimeOnlyHandler$1.execute(AbstractRuntimeOnlyHandler.java:59)
at org.jboss.as.controller@10.0.0.Final//org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:999)