flowable/flowable-engine · error · FlowableIllegalArgumentException

Involved groups are empty

Error message

Involved groups are empty

What it means

taskInvolvedGroups(Collection<String>) throws this error when the collection is non-null but empty. An empty collection cannot be turned into a meaningful IN-clause over identity links, so Flowable rejects it at query-build time.

Solutions

1. Guard with !involvedGroups.isEmpty() and omit the filter when the list is empty.
2. Decide the semantics of 'no groups': return an empty result immediately, or drop the group criterion entirely.
3. Before splitting a comma-separated string, trim and check for blank input.

Example fix

// before
query.taskInvolvedGroups(groups); // throws when groups is empty

// after
if (groups != null && !groups.isEmpty()) {
    query.taskInvolvedGroups(groups);
}

if (involvedGroups != null && !involvedGroups.isEmpty()) {
    historicTaskInstanceQuery.taskInvolvedGroups(involvedGroups);
} else {
    // no groups: either return empty result or omit this criterion
}

boolean hasGroups(Collection<String> groups) {
    return groups != null && !groups.isEmpty();
}

try {
    query.taskInvolvedGroups(groups);
} catch (FlowableIllegalArgumentException e) {
    // empty list: short-circuit or drop the filter
    return Collections.emptyList();
}

When it happens

Trigger: Calling taskInvolvedGroups(Collections.emptyList()) or a list reduced to zero elements by filtering (e.g. user is in no groups, or all groups were filtered out).

Common situations: Users with no group memberships; group lists filtered by tenant/type that end up empty; splitting an empty or blank string into a list.

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

• Candidate group list is empty
• Candidate group is null
• Candidate group list is empty
• Candidate group list is null
• Candidate user is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/077111a74c442cf8. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-task-service/src/main/java/org/flowable/task/service/impl/HistoricTaskInstanceQueryImpl.java:1961

        if (involvedUser == null) {
            throw new FlowableIllegalArgumentException("involved user is null");
        }

        if (inOrStatement) {
            this.currentOrQueryObject.involvedUser = involvedUser;
        } else {
            this.involvedUser = involvedUser;
        }
        return this;
    }

    @Override
    public HistoricTaskInstanceQuery taskInvolvedGroups(Collection<String> involvedGroups) {
        if (involvedGroups == null) {
            throw new FlowableIllegalArgumentException("Involved groups are null");
        }
        if (involvedGroups.isEmpty()) {
            throw new FlowableIllegalArgumentException("Involved groups are empty");
        }
        if (inOrStatement) {
            this.currentOrQueryObject.involvedGroups = involvedGroups;
        } else {
            this.involvedGroups = involvedGroups;
        }
        return this;
    }

    @Override
    public HistoricTaskInstanceQuery ignoreAssigneeValue() {
        if (inOrStatement) {
            this.currentOrQueryObject.ignoreAssigneeValue = true;
        } else {
            this.ignoreAssigneeValue = true;
        }
        return this;
    }

View on GitHub (pinned to d6d39ce1c6)