flowable/flowable-engine · error · FlowableIllegalArgumentException

Task name list is empty

Error message

Task name list is empty

What it means

Flowable throws this FlowableIllegalArgumentException when TaskQuery.taskNameIn is given an empty collection. An empty IN list would generate invalid or pointless SQL, so Flowable rejects it during query construction, after the null check.

Source

Thrown at modules/flowable-task-service/src/main/java/org/flowable/task/service/impl/TaskQueryImpl.java:256

        if (name == null) {
            throw new FlowableIllegalArgumentException("Task name is null");
        }

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

    @Override
    public TaskQuery taskNameIn(Collection<String> nameList) {
        if (nameList == null) {
            throw new FlowableIllegalArgumentException("Task name list is null");
        }
        if (nameList.isEmpty()) {
            throw new FlowableIllegalArgumentException("Task name list is empty");
        }
        for (String name : nameList) {
            if (name == null) {
                throw new FlowableIllegalArgumentException("None of the given task names can be null");
            }
        }

        if (name != null) {
            throw new FlowableIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and name");
        }
        if (nameLike != null) {
            throw new FlowableIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and nameLike");
        }
        if (nameLikeIgnoreCase != null) {
            throw new FlowableIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and nameLikeIgnoreCase");
        }

        if (orActive) {

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Check isEmpty() before calling taskNameIn and omit the filter when the list is empty.
2. Decide semantics explicitly: an empty selection usually means 'no filter' or 'no results' - implement whichever is intended.
3. Short-circuit and return an empty result set yourself if empty selection must mean zero results.
4. Make the UI/API forbid submitting a name filter with zero entries.

Example fix

// before
query.taskNameIn(selectedNames); // throws when selectedNames is empty
// after
if (selectedNames != null && !selectedNames.isEmpty()) {
    query.taskNameIn(selectedNames);
} // else: no name filter applied

if (names != null && !names.isEmpty()) {
    query.taskNameIn(names);
} else if (names != null) {
    return Collections.emptyList(); // empty selection means no matches by design
}

boolean isNonEmpty(Collection<?> c) { return c != null && !c.isEmpty(); }

try {
    query.taskNameIn(names);
} catch (FlowableIllegalArgumentException e) {
    if (e.getMessage().equals("Task name list is empty")) {
        log.warn("Empty name list; returning no results");
        return Collections.emptyList();
    }
    throw e;
}

When it happens

Trigger: Calling createTaskQuery().taskNameIn(Collections.emptyList()) or taskNameIn(new ArrayList<>()) - any collection with size 0.

Common situations: Dynamic filters where the user selected no names; upstream filtering (e.g. by tenant or permission) removed all entries from the list before the query was built.

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

• Could not find an app definition with id '<appDefinitionId>
• Could not find a deployment with id '<deploymentId>
• ids is an empty collection
• callbackIds is null or empty
• Error retrieving app engine info

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/948121a703cfac5e. Report an issue: GitHub.