flowable/flowable-engine · error · FlowableIllegalArgumentException

Event type cannot be null.

Error message

Event type cannot be null.

What it means

Argument guard in FlowableEventSupport.dispatchEvent: the event object exists but its getType() returns null. The dispatcher routes events to listeners by type, so an event without a type cannot be delivered and is rejected.

Solutions

1. Set a FlowableEventType on every custom event before dispatching
2. Reuse the engine's standard event types or well-formed custom type constants

When it happens

Trigger: Thrown at modules/flowable-engine-common/src/main/java/org/flowable/common/engine/impl/event/FlowableEventSupport.java:93 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/ead8cd3d0a39aa66. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-engine-common/src/main/java/org/flowable/common/engine/impl/event/FlowableEventSupport.java:93

            }
        }
    }

    public void removeEventListener(FlowableEventListener listenerToRemove) {
        eventListeners.remove(listenerToRemove);

        for (List<FlowableEventListener> listeners : typedListeners.values()) {
            listeners.remove(listenerToRemove);
        }
    }

    public void dispatchEvent(FlowableEvent event) {
        if (event == null) {
            throw new FlowableIllegalArgumentException("Event cannot be null.");
        }

        if (event.getType() == null) {
            throw new FlowableIllegalArgumentException("Event type cannot be null.");
        }

        // Call global listeners
        if (!eventListeners.isEmpty()) {
            for (FlowableEventListener listener : eventListeners) {
                dispatchEvent(event, listener);
            }
        }

        // Call typed listeners, if any
        List<FlowableEventListener> typed = typedListeners.get(event.getType());
        if (typed != null && !typed.isEmpty()) {
            for (FlowableEventListener listener : typed) {
                dispatchEvent(event, listener);
            }
        }
    }

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