flowable/flowable-engine · error · FlowableIllegalArgumentException

Candidate group list is null

Error message

Candidate group list is null

What it means

TaskQueryImpl.taskCandidateGroupIn() throws this when the candidateGroups collection is null. The IN-style filter requires an actual list of group ids to build its query criterion. The fail-fast check prevents malformed SQL and confusing downstream failures.

Solutions

1. Pass a non-null collection of group ids to taskCandidateGroupIn().
2. Null-check the collection first and skip the filter (or return empty result) when absent.
3. Initialize the collection at its source; remember empty lists trigger a separate error.
4. Fix the upstream code that returns null instead of a populated list.

Example fix

// before
TaskQuery query = taskService.createTaskQuery().taskCandidateGroupIn(candidateGroups);
// after
TaskQuery query = taskService.createTaskQuery();
if (candidateGroups != null && !candidateGroups.isEmpty()) {
    query = query.taskCandidateGroupIn(candidateGroups);
}

if (candidateGroups == null) {
    throw new IllegalArgumentException("candidateGroups must be non-null before taskCandidateGroupIn()");
}
query.taskCandidateGroupIn(candidateGroups);

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

try {
    query.taskCandidateGroupIn(groups);
} catch (FlowableIllegalArgumentException e) {
    logger.warn("Invalid candidate group list: {}", e.getMessage());
    query = taskService.createTaskQuery();
}

When it happens

Trigger: Calling taskQuery.taskCandidateGroupIn(null), e.g. when the list comes from a method that returned null, an unset field, or a config lookup that missed.

Common situations: Identity-provider lookup returned null groups; collection field not initialized; dynamic query composition passing a possibly-null variable.

Related errors

• Candidate group is null
• Assignee is null
• Assignee is null
• AssigneeLike is null
• AssigneeLike is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/9b2bd492e7e00627. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-task-service/src/main/java/org/flowable/task/service/impl/TaskQueryImpl.java:660

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

        if (orActive) {
            currentOrQueryObject.bothCandidateAndAssigned = true;
            currentOrQueryObject.userIdForCandidateAndAssignee = userIdForCandidateAndAssignee;
        } else {
            this.bothCandidateAndAssigned = true;
            this.userIdForCandidateAndAssignee = userIdForCandidateAndAssignee;
        }

        return this;
    }

    @Override
    public TaskQuery 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");
        }

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

        if (orActive) {
            currentOrQueryObject.candidateGroups = candidateGroups;
        } else {
            this.candidateGroups = candidateGroups;
        }
        return this;
    }

View on GitHub (pinned to d6d39ce1c6)