NullPointerException querying the process' variables from an aborted process instance in BPM Suite 6.3

Issue

We use Kie Server for process execution and when we try to access an aborted process variables using the following REST endpoint:

http://localhost:8080/kie-server/services/rest/server/containers/{containerID}/processes/instances/{instanceId}/variables

We face the following exception:

ERROR [org.kie.server.remote.rest.jbpm.ProcessResource] (http-localhost.localdomain/127.0.0.1:8080-5) Unexpected error during processing null: java.lang.NullPointerException
    at org.jbpm.kie.services.impl.ProcessServiceImpl.getProcessInstanceVariables(ProcessServiceImpl.java:324) [jbpm-kie-services-6.4.0.Final-redhat-3.jar:6.4.0.Final-redhat-3]
    at org.kie.server.services.jbpm.ProcessServiceBase.getProcessInstanceVariables(ProcessServiceBase.java:260) [kie-server-services-jbpm-6.4.0.Final-redhat-3.jar:6.4.0.Final-redhat-3]
    at org.kie.server.remote.rest.jbpm.ProcessResource.getProcessInstanceVariables(ProcessResource.java:338) [kie-server-rest-jbpm-6.4.0.Final-redhat-3.jar:6.4.0.Final-redhat-3]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_60]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) [rt.jar:1.7.0_60]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_60]
    at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_60]
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:168) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:269) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:227) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:216) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:561) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:543) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:128) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50) [resteasy-jaxrs-2.3.12.Final-redhat-1-bz-1313482.jar:]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-2.jar:1.0.2.Final-redhat-2]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:231) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:512) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169) [jboss-as-web-7.5.6.Final-redhat-2.jar:7.5.6.Final-redhat-2]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:150) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:400) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:854) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:653) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.12.Final-redhat-1.jar:7.5.12.Final-redhat-1]
    at java.lang.Thread.run(Thread.java:745) [rt.jar:1.7.0_60]