flowable/flowable-engine · error · org.flowable.common.engine.api.FlowableIllegalArgumentException

taskId is empty

Error message

taskId is empty

What it means

InternalVariableInstanceQueryImpl.taskId(String) throws FlowableIllegalArgumentException when the given taskId is null or an empty string. The variable-instance query API requires a non-empty task id to filter variables by task; passing blank input would produce a broken or full-table query, so the builder rejects it eagerly. This fail-fast validation happens at query-construction time, before any database access.

Solutions

1. Ensure a non-empty task id is resolved before building the query
2. Check the upstream source of the task id for empty/blank values
3. If the goal is 'variables not tied to a task', call withoutTaskId() instead of passing an empty id

Example fix

// before
query.taskId(task.getId()); // NPE/empty when task not yet persisted
// after
if (task != null && task.getId() != null) {
    query.taskId(task.getId());
} else {
    query.withoutTaskId();
}

if (taskId == null || taskId.isEmpty()) { throw new IllegalArgumentException("taskId must be non-empty before querying"); }

boolean hasTaskId(String id) { return id != null && !id.isEmpty(); }

try { query.taskId(taskId); } catch (FlowableIllegalArgumentException e) { log.warn("Invalid taskId for variable query", e); return Collections.emptyList(); }

When it happens

Trigger: Calling internalVariableInstanceQuery taskId(null) or taskId("") — e.g. a task id variable that was never initialized, or a value derived from an empty JSON/HTTP field.

Common situations: Task id fetched from an upstream API or form field that is blank; refactor left the id unset; whitespace-only strings (StringUtils.isEmpty treats only null and "" as empty, so " " passes and may return no results).

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• executionId is empty
• None of the given process categories can be null
• processInstanceId is empty
• scopeId is empty
• Task id list is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/b5fbe0449d9958aa. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-variable-service/src/main/java/org/flowable/variable/service/impl/InternalVariableInstanceQueryImpl.java:68

    protected boolean withoutSubScopeId;
    protected String scopeType;
    protected Collection<String> scopeTypes;
    protected String name;
    protected Collection<String> names;

    @Override
    public InternalVariableInstanceQuery id(String id) {
        if (StringUtils.isEmpty(id)) {
            throw new FlowableIllegalArgumentException("id is empty");
        }
        this.id = id;
        return this;
    }

    @Override
    public InternalVariableInstanceQuery taskId(String taskId) {
        if (StringUtils.isEmpty(taskId)) {
            throw new FlowableIllegalArgumentException("taskId is empty");
        }

        if (withoutTaskId) {
            throw new FlowableIllegalArgumentException("Cannot combine taskId(String) with withoutTaskId() in the same query");
        }

        this.taskId = taskId;
        return this;
    }

    @Override
    public InternalVariableInstanceQuery taskIds(Collection<String> taskIds) {
        if (taskIds == null || taskIds.isEmpty()) {
            throw new FlowableIllegalArgumentException("taskIds is null or empty");
        }

        if (withoutTaskId) {
            throw new FlowableIllegalArgumentException("Cannot combine taskIds(Collection) with withoutTaskId() in the same query");

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