Activiti/Activiti · error · ActivitiIllegalArgumentException

Variable of type ' ' is not allowed in JsonPatch mapping…

Error message

Variable %s of type '%s' is not allowed in JsonPatch mapping. Only string and integer types are allowed

What it means

Thrown by replaceVariableIfSupported when a variable referenced in a JSON Patch mapping path has a type other than string or integer. Only those two types are supported for placeholder substitution in patch paths; other types (boolean, date, json, etc.) are rejected to avoid ambiguous path rendering.

Solutions

Change the variable's declared type to string or integer in the process/extensions definition
Convert the value into a new string/integer variable and reference that in the patch path
Cast the incoming connector output to a supported type before storing it in the variable

Example fix

// before
execution.setVariable("orderId", 12345L); // long type
// after
execution.setVariable("orderId", String.valueOf(12345L)); // string type

Defensive patterns

Strategy: validation

Validate before calling

VariableDefinition def = extensions.getPropertyByName("orderId");
String t = def.getType().toLowerCase();
if (!("string".equals(t) || "integer".equals(t))) throw new IllegalStateException("orderId type must be string or integer");

Type guard

boolean patchSafeType(VariableDefinition d) {
    String t = d.getType() == null ? "" : d.getType().toLowerCase();
    return "string".equals(t) || "integer".equals(t);
}

Try / catch

try {
    outcome = task.complete();
} catch (ActivitiIllegalArgumentException e) {
    if (e.getMessage().contains("Only string and integer types are allowed")) {
        // convert the variable to a supported type and retry
    }
}

Prevention

Declare variables used in JSON Patch paths explicitly as string or integer in the model
Avoid type-changing refactors on variables referenced by mappings
Convert non-supported types (long, boolean, date) into helper string variables before mapping

When it happens

Trigger: An output mapping path like '/items/$orderId' where 'orderId' is defined but its variable type (per the extensions/variable definition) is e.g. boolean, long, or date.

Common situations: Changing a variable's type in the model (e.g. integer to long) without updating the mapping; the variable was auto-created with an inferred type; migrating from an older process version where the variable was a string.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of Activiti/Activiti@56435b1a97 (2026-09-09). Data as JSON: /api/errors/083d7f37e7e322d8. Report an issue: GitHub.

Appendix: source

Thrown at activiti-core/activiti-api-impl/activiti-api-process-runtime-impl/src/main/java/org/activiti/runtime/api/impl/ExtensionsVariablesMappingProvider.java:289

        }

        VariableDefinition propertyObj = extensions.getPropertyByName(variableName);
        return replaceVariableIfSupported(propertyObj.getValue(), propertyObj.getType(), variableName);
    }

    private String replaceVariableIfSupported(Object value, String type, String originalProperty) {
        if (value == null || StringUtils.isBlank(value.toString())) {
            throw new ActivitiIllegalArgumentException(
                String.format("Path variable $%s used in JsonPatch mapping should not be empty", originalProperty)
            );
        }

        String typeLowerCase = type.toLowerCase();
        if ("string".equals(typeLowerCase) || "integer".equals(typeLowerCase)) {
            return value.toString();
        }

        throw new ActivitiIllegalArgumentException(
            String.format(
                "Variable %s of type '%s' is not allowed in JsonPatch mapping. Only string and integer types are allowed",
                originalProperty,
                type
            )
        );
    }

    private void initializePath(JsonNode oldNode, JsonNode patchNode) {
        for (JsonNode patch : patchNode) {
            String path = patch.get("path").asString();
            String[] properties = path.split("/");

            JsonNode currentNode = oldNode;

            for (int i = 1; i < properties.length; i++) {
                String property = properties[i];
                if (isArrayElementPath(i, properties, property)) {

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