flowable/flowable-engine · error · FlowableIllegalArgumentException

taskId is null

Error message

taskId is null

What it means

VariableInstanceQuery.taskId(String) requires a non-null task id. Passing null throws FlowableIllegalArgumentException immediately because filtering variables by an absent task is invalid. This is a query-build-time validation; no query executes.

Solutions

1. Validate the task id is non-null before building the query
2. Only call taskId() when a task id is actually available; use a different filter otherwise
3. Ensure the id source (e.g. DelegateTask.getId()) is used in a task-scoped context

Example fix

// before
query.taskId(taskId); // may be null
// after
if (taskId != null) {
    query.taskId(taskId);
}

if (taskId == null) {
    throw new IllegalArgumentException("taskId is required");
}

boolean hasTaskId(String taskId) { return taskId != null && !taskId.isBlank(); }

try {
    query.taskId(taskId);
} catch (FlowableIllegalArgumentException e) {
    if (e.getMessage().equals("taskId is null")) {
        // skip or use alternative query
    } else { throw e; }
}

When it happens

Trigger: Passing a null taskId, typically from an uninitialized variable, a map lookup that missed, or a service method forwarding an optional task id as null.

Common situations: Task id looked up from an execution/process context where the current scope is not task-based (e.g. a service task, not a user task), yielding null.

Related errors

• executionIds is null
• taskIds is null
• Cannot use executionId together with excludeLocalVariables
• Cannot use executionIds together with excludeLocalVariables
• Cannot use taskId together with excludeTaskVariables

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/679010c95ea16fbe. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-variable-service/src/main/java/org/flowable/variable/service/impl/VariableInstanceQueryImpl.java:121

        if (executionIds.isEmpty()) {
            throw new FlowableIllegalArgumentException("Set of executionIds is empty");
        }
        if (excludeLocalVariables) {
            throw new FlowableIllegalArgumentException("Cannot use executionIds together with excludeLocalVariables");
        }
        this.executionIds = executionIds;
        return this;
    }

    public VariableInstanceQuery activityInstanceId(String activityInstanceId) {
        this.activityInstanceId = activityInstanceId;
        return this;
    }

    @Override
    public VariableInstanceQuery taskId(String taskId) {
        if (taskId == null) {
            throw new FlowableIllegalArgumentException("taskId is null");
        }
        if (excludeTaskRelated) {
            throw new FlowableIllegalArgumentException("Cannot use taskId together with excludeTaskVariables");
        }
        if (excludeLocalVariables) {
            throw new FlowableIllegalArgumentException("Cannot use taskIds together with excludeLocalVariables");
        }
        this.taskId = taskId;
        return this;
    }

    @Override
    public VariableInstanceQueryImpl taskIds(Set<String> taskIds) {
        if (taskIds == null) {
            throw new FlowableIllegalArgumentException("taskIds is null");
        }
        if (taskIds.isEmpty()) {
            throw new FlowableIllegalArgumentException("Set of taskIds is empty");

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