Unable to marshall JaxbCommandsRequest

Issue

• When using SetProcessInstanceVariablesCommand or StartProcessCommand remotely, via /execute endpoint, following exception is visible in the logs:

org.kie.services.client.serialization.SerializationException: Unable to marshall JaxbCommandsRequest instance.
    at org.kie.services.client.serialization.JaxbSerializationProvider.serialize(JaxbSerializationProvider.java:155)
....
Caused by: java.lang.NullPointerException
    at org.drools.core.xml.jaxb.util.JaxbMapAdapter.marshal(JaxbMapAdapter.java:42)
    at org.drools.core.xml.jaxb.util.JaxbMapAdapter.marshal(JaxbMapAdapter.java:31)
    at com.sun.xml.bind.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:76)
    ... 39 more

• While are trying to trigger BPMN2 process using JMS Remote API , it throws the following error messages.

org.kie.services.client.serialization.SerializationException: Unable to marshall JaxbCommandsRequest instance