Description of problem:
Impossible to export to PDF and to PNG project with long chain of elements.

Version-Release number of selected component (if applicable):
6.2.GA

How reproducible:
always

Steps to Reproduce:
1. Import attached process
2. Try to export to PNG or PDF
3. Try to click "Share process PDF/PNG"

Actual results:
point 2: new tab is open but downloading is not started, server log is clear
point 3: Message "Failed to create the process PDF/PNG" shown, server log contain NullPointerException exception:

14:20:17,096 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/business-central].[TransformerServlet]] (http-/127.0.0.1:8080-5) JBWEB000236: Servlet.service() for servlet TransformerServlet threw exception: java.lang.NullPointerException
at org.jbpm.designer.web.server.TransformerServlet.doPost(TransformerServlet.java:142) [jbpm-designer-backend-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:754) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-2.jar:1.0.2.Final-redhat-2]
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-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.uberfire.ext.security.server.SecureHeadersFilter.doFilter(SecureHeadersFilter.java:53) [uberfire-servlet-security-0.7.4.Final-redhat-4.jar:0.7.4.Final-redhat-4]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.uberfire.ext.security.server.SecurityIntegrationFilter.doFilter(SecurityIntegrationFilter.java:45) [uberfire-servlet-security-0.7.4.Final-redhat-4.jar:0.7.4.Final-redhat-4]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:231) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:512) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.5.4.Final-redhat-4.jar:7.5.4.Final-redhat-4]
at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.5.4.Final-redhat-4.jar:7.5.4.Final-redhat-4]
at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169) [jboss-as-web-7.5.4.Final-redhat-4.jar:7.5.4.Final-redhat-4]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:150) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:419) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:854) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:653) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
at java.lang.Thread.run(Thread.java:745) [rt.jar:1.7.0_79]

Expected results:
No problems with long process occure.

Additional info:
If you reduce attached process export will work as expected.