Nullpointerexception thrown from PerProcessInstanceRuntimeManager.releaseAndCleanLock

Issue

• Given a parent process which has a sub process (independent=false) and then another sub process (independent=false). When the sub-sub process is terminated the following stack trace is thrown:

ERROR [org.kie.server.remote.rest.jbpm.ProcessResource] (http-10.128.20.30:8080-1) [, , , ] Unexpected error during processing null: java.lang.NullPointerException
        at org.jbpm.runtime.manager.impl.PerProcessInstanceRuntimeManager.releaseAndCleanLock(PerProcessInstanceRuntimeManager.java:630)
        at org.jbpm.runtime.manager.impl.PerProcessInstanceRuntimeManager.disposeRuntimeEngine(PerProcessInstanceRuntimeManager.java:239)
        at org.jbpm.kie.services.impl.ProcessServiceImpl.disposeRuntimeEngine(ProcessServiceImpl.java:577)
        at org.jbpm.kie.services.impl.ProcessServiceImpl.abortProcessInstance(ProcessServiceImpl.java:154)
        at org.jbpm.kie.services.impl.ProcessServiceImpl.abortProcessInstances(ProcessServiceImpl.java:161)
        at org.kie.server.services.jbpm.ProcessServiceBase.abortProcessInstances(ProcessServiceBase.java:134)
        at org.kie.server.remote.rest.jbpm.ProcessResource.abortProcessInstances(ProcessResource.java:158)