Process image doesn't get load in BPMS 6.0.x

Issue

• When trying to load process image on BPMS 6.0.x it doesn't show up and the following error is thrown.

Could not open requested business process due to processing errors.
Empty process was loaded instead.
Click on the Details tab below to view error details.

• The issue comes with only existing processes, and newly created processes can be opened up. Even those processes whose image can't open are accessible to perform the start, stop operations on it's instances through REST APIs. So apparently issue is just with rendering of process image. The following stack trace can be seen in the console.

java.lang.Exception: org.eclipse.emf.ecore.resource.Resource$IOWrappedException: Unresolved reference 'null'. (inputStream://dummyUriWithValidSuffix.xml, 44, 48)
    at org.jbpm.designer.web.profile.impl.JbpmProfileImpl.getDefinitions(JbpmProfileImpl.java:318)
    at org.jbpm.designer.web.profile.impl.JbpmProfileImpl$2.parseModel(JbpmProfileImpl.java:245)
    at org.jbpm.designer.web.repository.impl.UUIDBasedJbpmRepository.load(UUIDBasedJbpmRepository.java:37)
    at org.jbpm.designer.web.server.UUIDBasedRepositoryServlet.doGet(UUIDBasedRepositoryServlet.java:116)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.jboss.solder.servlet.exception.CatchExceptionFilter.doFilter(CatchExceptionFilter.java:65)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.jboss.solder.servlet.event.ServletEventBridgeFilter.doFilter(ServletEventBridgeFilter.java:74)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.jbpm.designer.web.filter.impl.PluggableFilter.doFilter(PluggableFilter.java:70)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.uberfire.security.server.UberFireSecurityFilter.doFilter(UberFireSecurityFilter.java:266)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:407)
    at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50)
    at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50)
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:145)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97)
    at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:408)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:336)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:653)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:920)
    at java.lang.Thread.run(Thread.java:662)
Caused by: org.eclipse.emf.ecore.resource.Resource$IOWrappedException: Unresolved reference 'null'. (inputStream://dummyUriWithValidSuffix.xml, 44, 48)
    at org.eclipse.emf.ecore.xmi.impl.XMLLoadImpl.handleErrors(XMLLoadImpl.java:83)
    at org.eclipse.emf.ecore.xmi.impl.XMLLoadImpl.load(XMLLoadImpl.java:191)
    at org.eclipse.emf.ecore.xmi.impl.XMLResourceImpl.doLoad(XMLResourceImpl.java:180)
    at org.eclipse.emf.ecore.resource.impl.ResourceImpl.load(ResourceImpl.java:1494)
    at org.jbpm.designer.web.profile.impl.JbpmProfileImpl.getDefinitions(JbpmProfileImpl.java:298)
    ... 34 more
Caused by: org.eclipse.emf.ecore.xmi.UnresolvedReferenceException: Unresolved reference 'null'. (inputStream://dummyUriWithValidSuffix.xml, 44, 48)
    at org.eclipse.emf.ecore.xmi.impl.XMLHandler.handleForwardReferences(XMLHandler.java:1154)
    at org.eclipse.emf.ecore.xmi.impl.XMLHandler.endDocument(XMLHandler.java:1228)
    at org.apache.xerces.parsers.AbstractSAXParser.endDocument(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentScannerImpl.endEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityManager.endEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityScanner.load(Unknown Source)
    at org.apache.xerces.impl.XMLEntityScanner.skipSpaces(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentScannerImpl$TrailingMiscDispatcher.dispatch(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
    at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
    at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
    at org.apache.xerces.jaxp.SAXParserImpl.parse(Unknown Source)
    at org.eclipse.emf.ecore.xmi.impl.XMLLoadImpl.load(XMLLoadImpl.java:181)
    ... 37 more