flowable/flowable-engine · error · ActivitiIllegalArgumentException

Task name list is empty

Error message

Task name list is empty

What it means

HistoricTaskInstanceQueryImpl.taskNameIn() throws ActivitiIllegalArgumentException when the task name list is non-null but empty. An empty IN list is invalid, so at least one task name must be supplied. Additionally, taskNameIn is mutually exclusive with taskName/taskNameLike, which the library checks right after this guard.

Solutions

1. Check !names.isEmpty() before calling taskNameIn; skip the filter when empty.
2. Verify how the list is built — ensure at least one name is collected before query execution.
3. Ensure you are not mixing taskNameIn with taskName or taskNameLike, which throws a separate invalid-usage error.

Example fix

// before
query.taskNameIn(names); // empty list

// after
if (names != null && !names.isEmpty()) {
    query.taskNameIn(names);
}

if (names != null && !names.isEmpty()) {
    if (useNameEquals) { throw new IllegalStateException("taskNameIn is mutually exclusive with taskName"); }
    query.taskNameIn(names);
}

static boolean canApplyNameIn(List<String> names, String taskName, String taskNameLike) { return names != null && !names.isEmpty() && taskName == null && taskNameLike == null; }

try {
    query.taskNameIn(names);
} catch (org.activiti.engine.ActivitiIllegalArgumentException e) {
    // covers both empty-list and taskName/taskNameLike conflicts
    log.warn("Invalid task name filter: {}", e.getMessage());
}

When it happens

Trigger: Calling historicTaskInstanceQuery.taskNameIn(new ArrayList<>()) or any empty List<String>.

Common situations: Search box with multiple keywords that the user left blank; splitting an empty string into an empty list ("".split(",") nuances aside); passing an empty filter set from a saved search.

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

• Process category list is empty
• None of the given process categories can be null
• None of the given process instance ids can be null
• Process category list is null
• Process definition category is null

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/63c55b5d0f26d5de. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/HistoricTaskInstanceQueryImpl.java:381

    }

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

    @Override
    public HistoricTaskInstanceQuery taskNameIn(List<String> taskNameList) {
        if (taskNameList == null) {
            throw new ActivitiIllegalArgumentException("Task name list is null");
        }
        if (taskNameList.isEmpty()) {
            throw new ActivitiIllegalArgumentException("Task name list is empty");
        }

        if (taskName != null) {
            throw new ActivitiIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and taskName");
        }
        if (taskNameLike != null) {
            throw new ActivitiIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and taskNameLike");
        }
        if (taskNameLikeIgnoreCase != null) {
            throw new ActivitiIllegalArgumentException("Invalid query usage: cannot set both taskNameIn and taskNameLikeIgnoreCase");
        }

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

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