Assume that you have working deployment with a custom MSC service wrapped into a SingletonService. When you are trying to access the value of the SingletonService, the SingletonService.getValue() call fails with NullPointerException iff the JBoss instance is listening on all interfaces, i.e. it is bound to 0.0.0.0 by using <inet-address value="0.0.0.0"/> or <any-address/> under <interface name="public"> in standalone-full-ha.xml.

It works when specifying an explicit IP.

Example: try the cluster-ha-singleton jboss-as-quickstart

Top of the stack trace:

java.lang.NullPointerException
at org.jboss.as.clustering.singleton.SingletonService.getValue(SingletonService.java:176)
at org.jboss.as.clustering.singleton.SingletonService.getValue(SingletonService.java:53)
at org.jboss.msc.service.ServiceControllerImpl.getValue(ServiceControllerImpl.java:1203)
[...]