Jack Q tao [http://community.jboss.org/people/qintao1203] created the discussion "How to setVariable after JPAKnowledgeService.loadStatefulKnowledgeSession" To view the discussion, visit: http://community.jboss.org/message/636928#636928 -------------------------------------------------------------- Hi all, I write some code to change variables of process  , but it can't work . The error info: java.lang.NullPointerException           at org.jbpm.process.instance.impl.ProcessInstanceImpl.getProcess(ProcessInstanceImpl.java:67)           at org.jbpm.process.instance.impl.ProcessInstanceImpl.getContextInstance(ProcessInstanceImpl.java:127)           at org.jbpm.workflow.instance.impl.WorkflowProcessInstanceImpl.setVariable(WorkflowProcessInstanceImpl.java:237)   My code :                     KnowledgeBase kbase = createKnowledgeBase();                     StatefulKnowledgeSession ksession =JPAKnowledgeService.loadStatefulKnowledgeSession(jbpm.getSessionId(), kbase, null, getEnv() );                     CommanWSHumanTaskHandler humanTaskHandler = new CommanWSHumanTaskHandler(ksession);                     humanTaskHandler.setClient(taskClientWrapper.getTaskClient());                     humanTaskHandler.setSessionId(ksession.getId());                     ksession.getWorkItemManager().registerWorkItemHandler("Human Task", humanTaskHandler);                     humanTaskHandler.connect();                     ProcessInstance pi = ksession.getProcessInstance(jbpm.getProcessId());                     Boolean isSign = (Boolean) ((WorkflowProcessInstance)pi).getVariable("isSign");                     List<String> list = (List<String>) ((WorkflowProcessInstance)pi).getVariable("signers");    //  *isSign* and *list*   are not null*.*                     ((WorkflowProcessInstance)pi).setVariable("isSign", true);        // throws exception                     ((WorkflowProcessInstance)pi).setVariable("signers", signers);                     ksession.insert(pi); I don't understand why.   and How to fix it. -------------------------------------------------------------- Reply to this message by going to Community [http://community.jboss.org/message/636928#636928] Start a new discussion in jBPM at Community [http://community.jboss.org/choose-container!input.jspa?contentType=1&...]