flowable/flowable-engine · error · FlowableIllegalArgumentException

Cannot convert event payload ${payloadInstanceValue} to type

Error message

Cannot convert event payload ${payloadInstanceValue} to type 'double'

What it means

FlowableIllegalArgumentException thrown by EventPayloadToJsonStringSerializer.serialize when a payload instance declared as type 'double' is neither a Number nor a String, so it cannot be converted to a JSON double. This happens while serializing an event payload to JSON for transmission/storage.

Source

Thrown at modules/flowable-event-registry/src/main/java/org/flowable/eventregistry/impl/serialization/EventPayloadToJsonStringSerializer.java:71

                continue;
            }

            String definitionType = payloadInstance.getDefinitionType();
            Object payloadInstanceValue = payloadInstance.getValue();

            if (payloadInstanceValue != null) {

                if (EventPayloadTypes.STRING.equals(definitionType)) {
                    objectNode.put(payloadInstance.getDefinitionName(), payloadInstanceValue.toString());

                } else if (EventPayloadTypes.DOUBLE.equals(definitionType)) {

                    if (payloadInstanceValue instanceof Number) {
                        objectNode.put(payloadInstance.getDefinitionName(), ((Number) payloadInstanceValue).doubleValue());
                    } else if (payloadInstanceValue instanceof String) {
                        objectNode.put(payloadInstance.getDefinitionName(), Double.valueOf((String) payloadInstanceValue));
                    } else {
                        throw new FlowableIllegalArgumentException("Cannot convert event payload " + payloadInstanceValue + " to type 'double'");
                    }

                } else if (EventPayloadTypes.INTEGER.equals(definitionType)) {

                    if (payloadInstanceValue instanceof Number) {
                        objectNode.put(payloadInstance.getDefinitionName(), ((Number) payloadInstanceValue).intValue());
                    } else if (payloadInstanceValue instanceof String) {
                        objectNode.put(payloadInstance.getDefinitionName(), Integer.valueOf((String) payloadInstanceValue));
                    } else {
                        throw new FlowableIllegalArgumentException("Cannot convert event payload " + payloadInstanceValue + " to type 'integer'");
                    }

                } else if (EventPayloadTypes.LONG.equals(definitionType)) {

                    if (payloadInstanceValue instanceof Number) {
                        objectNode.put(payloadInstance.getDefinitionName(), ((Number) payloadInstanceValue).longValue());
                    } else if (payloadInstanceValue instanceof String) {
                        objectNode.put(payloadInstance.getDefinitionName(), Long.valueOf((String) payloadInstanceValue));

View on GitHub (pinned to d6d39ce1c6)

Solutions

Set the payload value as a Double/Number (or numeric String) matching the declared 'double' payload type.
Correct the event payload definition if the value is legitimately non-numeric (change type to 'string' or 'json').
Validate/coerce payload values before calling the serializer / publishing the event.

Example fix

// before
EventPayloadInstance p = ...; // declared 'double'
p.setValue("value", complexObject);
// after
p.setValue("value", Double.parseDouble(objectValue.toString()));

Defensive patterns

Strategy: type-guard

Validate before calling

Object v = payloadValue; if (!(v instanceof Number) && !(v instanceof String)) { throw new IllegalArgumentException("payload 'double' value must be Number or numeric String"); }

Type guard

boolean isDoubleCompatible(Object v) { return v instanceof Number || v instanceof String; }

Try / catch

try { serializer.serialize(eventInstance); } catch (FlowableIllegalArgumentException e) { LOG.error("payload type mismatch for double field: " + e.getMessage()); throw e; }

Prevention

Match Java value types to declared payload types when building event instances
Coerce numeric values to Double before publishing
Keep payload definitions and producers in sync via schema tests

When it happens

Trigger: Event payload definition declares type 'double' but the payload instance value is an incompatible object (e.g. Boolean, Map, POJO, or null-valued wrapper) when the event is serialized.

Common situations: Event instance built programmatically with wrong value types; upstream producer sending strings/objects that bypass type coercion; refactored payload models changing a field's Java type.

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 flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/b415c3607919ea15. Report an issue: GitHub.