Actually this issue is araising when I restart my development server.
Case is: I am trying get the assigned task list of User. From Task object when I am trying to get ProcessInstanceId and from this proessInstanceId I am trying to get RuleFlowProcess object. when getting RuleFlowProcess object I am getting the NullPointerException internally in the framework.
ProcessInstance processInstance =
ksession.getProcessInstance(task.getProcessInstanceId());
RuleFlowProcess process = (RuleFlowProcess) kbase.getProcess(processInstance.getProcessId()); // in this line I am getting the exception