flowable/flowable-engine · error · FlowableIllegalArgumentException

Task id should not be null

Error message

Task id should not be null

What it means

FlowableIllegalArgumentException thrown by GetRenderedTaskFormCmd.execute as a precondition check: the taskId supplied to the command is null. Nothing is looked up; the command fails fast because rendering a task form is impossible without a task id.

Solutions

1. Ensure a non-null task id is passed: obtain it from taskService.createTaskQuery()...singleResult().getId() or from a persisted TaskEntity.
2. Add a null/blank check in the calling code before invoking the form API.
3. If the task is created programmatically, call taskService.saveTask(task) first so it receives a database id.

Example fix

// before
String id = myTask != null ? myTask.getId() : null;
Object form = formService.getRenderedTaskForm(id);
// after
if (myTask == null || myTask.getId() == null) {
    throw new IllegalArgumentException("A persisted task is required");
}
Object form = formService.getRenderedTaskForm(myTask.getId());

if (taskId == null || taskId.isBlank()) {
    throw new IllegalArgumentException("taskId must be a persisted, non-null id");
}

boolean hasValidTaskId(Task t) { return t != null && t.getId() != null && !t.getId().isEmpty(); }

try {
    return formService.getRenderedTaskForm(taskId);
} catch (FlowableIllegalArgumentException e) {
    if (e.getMessage().contains("Task id should not be null")) { /* reject request before engine call next time */ }
}

When it happens

Trigger: Calling formService.getRenderedTaskForm(taskId) (with or without a form engine name) passing null — typically an uninitialized variable, a Task object whose getId() returned null, or an unsaved transient task.

Common situations: Passing task.getId() of a task created in Java but not yet saved through the task service; a mapping layer that dropped the id; forgetting to assign the result of taskService.createTaskQuery() before rendering the form.

Related errors

• Task '
• task is null
• taskId is null
• taskId is null
• taskId is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/be78cf20dd391623. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-engine/src/main/java/org/flowable/engine/impl/cmd/GetRenderedTaskFormCmd.java:51

 * @author Tom Baeyens
 * @author Joram Barrez
 */
public class GetRenderedTaskFormCmd implements Command<Object>, Serializable {

    private static final long serialVersionUID = 1L;
    protected String taskId;
    protected String formEngineName;

    public GetRenderedTaskFormCmd(String taskId, String formEngineName) {
        this.taskId = taskId;
        this.formEngineName = formEngineName;
    }

    @Override
    public Object execute(CommandContext commandContext) {

        if (taskId == null) {
            throw new FlowableIllegalArgumentException("Task id should not be null");
        }

        ProcessEngineConfigurationImpl processEngineConfiguration = CommandContextUtil.getProcessEngineConfiguration(commandContext);
        TaskEntity task = processEngineConfiguration.getTaskServiceConfiguration().getTaskService().getTask(taskId);
        if (task == null) {
            throw new FlowableObjectNotFoundException("Task '" + taskId + "' not found", Task.class);
        }

        FormHandlerHelper formHandlerHelper = processEngineConfiguration.getFormHandlerHelper();
        TaskFormHandler taskFormHandler = formHandlerHelper.getTaskFormHandlder(task);
        if (taskFormHandler != null) {

            FormEngine formEngine = processEngineConfiguration.getFormEngines().get(formEngineName);

            if (formEngine == null) {
                throw new FlowableException("No formEngine '" + formEngineName + "' defined process engine configuration");
            }

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