flowable/flowable-engine · error · ActivitiIllegalArgumentException

None of the given process categories can be null

Error message

None of the given process categories can be null

What it means

HistoricTaskInstanceQueryImpl.processCategoryIn() throws ActivitiIllegalArgumentException when any element of the category list is null. Since the list feeds an SQL IN clause, null entries are rejected. Remove nulls or fix the code that builds the list.

Solutions

1. Strip null entries: categories.removeIf(Objects::isNull) before calling.
2. Sanitize the config/source producing the categories so blanks become skips, not nulls.
3. Validate each category string (non-null, non-empty) when building the list.

Example fix

// before
query.processCategoryIn(categories); // contains nulls

// after
List<String> safe = categories.stream().filter(Objects::nonNull).collect(Collectors.toList());
if (!safe.isEmpty()) {
    query.processCategoryIn(safe);
}

List<String> safe = categories.stream().filter(c -> c != null && !c.trim().isEmpty()).collect(Collectors.toList());
if (!safe.isEmpty()) { query.processCategoryIn(safe); }

static boolean allNonNull(List<String> list) { return list != null && list.stream().allMatch(Objects::nonNull); }

try {
    query.processCategoryIn(categories);
} catch (org.activiti.engine.ActivitiIllegalArgumentException e) {
    log.error("processCategoryIn rejected: {}", e.getMessage());
    throw e; // programmer error, rethrow after logging
}

When it happens

Trigger: Calling historicTaskInstanceQuery.processCategoryIn(Arrays.asList("http://example.com/hr", null)).

Common situations: Reading category names from config files/DB rows where some entries are blank; mapping optional fields to list entries with nulls; JSON payloads containing null array items.

Related errors

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

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/46db10af93ddeb60. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/HistoricTaskInstanceQueryImpl.java:301

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

    @Override
    public HistoricTaskInstanceQuery processCategoryIn(List<String> processCategoryInList) {
        if (processCategoryInList == null) {
            throw new ActivitiIllegalArgumentException("Process category list is null");
        }
        if (processCategoryInList.isEmpty()) {
            throw new ActivitiIllegalArgumentException("Process category list is empty");
        }
        for (String processCategory : processCategoryInList) {
            if (processCategory == null) {
                throw new ActivitiIllegalArgumentException("None of the given process categories can be null");
            }
        }

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

    @Override
    public HistoricTaskInstanceQuery processCategoryNotIn(List<String> processCategoryNotInList) {
        if (processCategoryNotInList == null) {
            throw new ActivitiIllegalArgumentException("Process category list is null");
        }
        if (processCategoryNotInList.isEmpty()) {
            throw new ActivitiIllegalArgumentException("Process category list is empty");

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