flowable/flowable-engine · error · FlowableIllegalArgumentException

Invalid query usage: cannot set both candidateGroup and…

Error message

Invalid query usage: cannot set both candidateGroup and candidateGroupIn

What it means

taskCandidateGroup(String) throws this error when the query already has candidateGroups (from taskCandidateGroupIn) set. The two filters are mutually exclusive: candidateGroup matches exactly one group while candidateGroupIn matches any of a list, and the SQL generator supports only one form per query object.

Solutions

1. Choose one filter: remove either the taskCandidateGroup(...) call or the taskCandidateGroupIn(...) call on the same query.
2. Use a fresh HistoricTaskInstanceQuery instance for each distinct filter combination.
3. Represent a single group as a one-element list and use taskCandidateGroupIn(Collections.singletonList(group)) exclusively.

Example fix

// before
query.taskCandidateGroupIn(groups);
query.taskCandidateGroup("backoffice"); // throws

// after
List<String> effectiveGroups = new ArrayList<>(groups);
effectiveGroups.add("backoffice");
query.taskCandidateGroupIn(effectiveGroups);

// choose ONE form before building the query
boolean useGroupList = groupList != null && !groupList.isEmpty();
if (useGroupList) {
    query.taskCandidateGroupIn(groupList);
} else if (candidateGroup != null) {
    query.taskCandidateGroup(candidateGroup);
}

boolean canSetCandidateGroup(HistoricTaskInstanceQueryImpl q) {
    return q.candidateGroups == null; // group list not yet set
}

try {
    query.taskCandidateGroup(candidateGroup);
} catch (FlowableIllegalArgumentException e) {
    throw new IllegalStateException(
        "Query already filters by candidateGroupIn; remove one of the two group filters", e);
}

When it happens

Trigger: Chaining .taskCandidateGroupIn(Arrays.asList("a","b")).taskCandidateGroup("a") — or the reverse order with taskCandidateGroup called before taskCandidateGroupIn — on the same HistoricTaskInstanceQuery instance.

Common situations: Building query filters dynamically where different code paths each set a candidate-group criterion; UIs that let users pick either a single group or a group list but accumulate conditions instead of replacing them.

Related errors

• Invalid query usage: cannot set both candidateGroupIn and…
• 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/51060bcf037bebec. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-task-service/src/main/java/org/flowable/task/service/impl/HistoricTaskInstanceQueryImpl.java:1908

            throw new FlowableIllegalArgumentException("Candidate user is null");
        }

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

    @Override
    public HistoricTaskInstanceQuery taskCandidateGroup(String candidateGroup) {
        if (candidateGroup == null) {
            throw new FlowableIllegalArgumentException("Candidate group is null");
        }

        if (candidateGroups != null) {
            throw new FlowableIllegalArgumentException("Invalid query usage: cannot set both candidateGroup and candidateGroupIn");
        }

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

    @Override
    public HistoricTaskInstanceQuery taskCandidateGroupIn(Collection<String> candidateGroups) {
        if (candidateGroups == null) {
            throw new FlowableIllegalArgumentException("Candidate group list is null");
        }

        if (candidateGroups.isEmpty()) {
            throw new FlowableIllegalArgumentException("Candidate group list is empty");

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