TaskEntity.getCandidates() NPE

[arkadi]

I'm trying to show task's candidate information in the GUI by invoking TaskEntity.getCandidates() in the following piece of code but then only NPE comes out

Caused by: java.lang.NullPointerException
    at org.activiti.engine.impl.persistence.entity.TaskEntity.getIdentityLinks(TaskEntity.java:339)
    at org.activiti.engine.impl.persistence.entity.TaskEntity.getCandidates(TaskEntity.java:281)
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Task t = engine.getTaskService()
    .createTaskQuery()
    .taskId(id).singleResult();
String names = assignee(t);

String assignee(Task task) {
    String assignee = task.getAssignee();
    if (assignee != null)
        return user(assignee);
    if (!(task instanceof TaskEntity))
        return null;
    List<String> candidates = new ArrayList<String>();
    for (IdentityLink c : ((TaskEntity) task).getCandidates()) {
        if (c.getGroupId() != null)
            candidates.add(group(c.getGroupId()));
        else if (c.getUserId() != null)
            candidates.add(user(c.getUserId()));
    }
    return join(candidates.toArray(strings), ", ");
}
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Activiti v5.6.
Is it me doing it wrong or I should raise an issue for that?
The required functionality is not exposed via interface, but as I learned from activiti-rest component, to obtain current process instance diagram you need to cast to impl, so my approach is legal until public API is created, I believe.

[jbarrez]

If it's not in the public API (ie .impl package), then things like this NPE can happen.

The public method to do what you want is on the taskService:  List<IdentityLink> getIdentityLinksForTask(String taskId);

[arkadi]

Thank you. That works. Somehow I missed the function while reading the API doc.