flowable/flowable-engine · error · ActivitiIllegalArgumentException

taskIds is null

Error message

taskIds is null

What it means

HistoricVariableInstanceQueryImpl.taskIds(Set<String>) validates its argument before use and throws ActivitiIllegalArgumentException when the passed set is null. A null set carries no task filter information, so the query would silently be wrong; the library fails fast instead. Pass a non-null, non-empty set of task IDs.

Solutions

1. Ensure the set is initialized (e.g. new HashSet<>()) before calling taskIds().
2. Guard the call: only invoke taskIds() when the set is non-null; skip the filter otherwise.
3. Fix the upstream source that produced null instead of an empty collection.

Example fix

// before
query.taskIds(taskIds);
// after
if (taskIds != null && !taskIds.isEmpty()) {
    query.taskIds(taskIds);
}

if (taskIds == null) { taskIds = java.util.Collections.emptySet(); }
if (!taskIds.isEmpty()) { query.taskIds(taskIds); }

boolean hasTaskIds(Set<String> s) { return s != null && !s.isEmpty(); }

try { query.taskIds(taskIds); } catch (org.activiti.engine.ActivitiIllegalArgumentException e) { throw new IllegalArgumentException("taskIds set must be non-null and non-empty", e); }

When it happens

Trigger: historyService.createHistoricVariableInstanceQuery().taskIds(null) — e.g. when a collection that was expected to hold task IDs is null (uninitialized variable, failed lookup, absent method parameter).

Common situations: Passing an optional task ID list straight into taskIds() without a null check; a repository/DAO returning null instead of an empty collection; NPE-avoidance refactor replacing direct dereference with this setter that then rejects null.

Related errors

• Business key is null
• Execution id is null
• Parent id is null
• Process definition keys is null
• Process definition version is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/c1b0daef5e3c273e. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/HistoricVariableInstanceQueryImpl.java:118

        return this;
    }

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

    @Override
    public HistoricVariableInstanceQueryImpl taskIds(Set<String> taskIds) {
        if (taskIds == null) {
            throw new ActivitiIllegalArgumentException("taskIds is null");
        }
        if (taskIds.isEmpty()) {
            throw new ActivitiIllegalArgumentException("Set of taskIds is empty");
        }
        if (excludeTaskRelated) {
            throw new ActivitiIllegalArgumentException("Cannot use taskIds together with excludeTaskVariables");
        }
        this.taskIds = taskIds;
        return this;
    }

    @Override
    public HistoricVariableInstanceQuery excludeTaskVariables() {
        if (taskId != null) {
            throw new ActivitiIllegalArgumentException("Cannot use taskId together with excludeTaskVariables");
        }
        if (taskIds != null) {
            throw new ActivitiIllegalArgumentException("Cannot use taskIds together with excludeTaskVariables");

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