Description of problem:

Following code will throw NPE when ts.getTasksByProcessInstance(pi.getId()); is called.

<code-snip>
public class JbpmExecutor {


    public RuntimeEngine newRuntime(String... processes) throws Exception {
        RuntimeEnvironmentBuilder builder = RuntimeEnvironmentBuilder.getEmpty()
                .addConfiguration("drools.processSignalManagerFactory", DefaultSignalManagerFactory.class.getName())
                .addConfiguration("drools.processInstanceManagerFactory", DefaultProcessInstanceManagerFactory.class.getName());
        
        for (String process : processes) {
        	builder.addAsset(ResourceFactory.newClassPathResource(process), ResourceType.BPMN2);
        }
        
//        for (String ruleFile : ruleFiles) {
//            builder.addAsset(ResourceFactory.newClassPathResource(ruleFile), ResourceType.DRL);
//        }
        
        RuntimeManager manager = RuntimeManagerFactory.Factory.get().newSingletonRuntimeManager(builder.get(), "Singleton " + UUID.randomUUID().toString());
        RuntimeEngine runtime = manager.getRuntimeEngine(EmptyContext.get());
        
        return runtime;
    }

    public static void main(String ... args) throws Exception {
		JbpmExecutor executor = new JbpmExecutor();
		RuntimeEngine runtime = executor.newRuntime("xxx.bpmn2");
		
		ProcessInstance pi = runtime.getKieSession().startProcess("BPMN2IntermediateThrowEscalationEvent");
		System.out.println(pi.getState() == ProcessInstance.STATE_COMPLETED);
		
		TaskService ts = runtime.getTaskService();
		// Throws NPE. I would consider this a bug which is not yet reported. 
		System.out.println(ts.getTasksByProcessInstanceId(pi.getId()));
	}
    
}
</code-snip>