flowable/flowable-engine · error · FlowableIllegalArgumentException

event is null

Error message

event is null

What it means

DispatchEventCommand validates that the FlowableEvent to dispatch is non-null and throws FlowableIllegalArgumentException otherwise. The event is then handed to the engine's FlowableEventDispatcher. It exists so a null event fails fast rather than crashing inside dispatcher internals.

Source

Thrown at modules/flowable-engine/src/main/java/org/flowable/engine/impl/cmd/DispatchEventCommand.java:40

import org.flowable.engine.impl.util.CommandContextUtil;

/**
 * Command that dispatches an event.
 * 
 * @author Frederik Heremans
 */
public class DispatchEventCommand implements Command<Void> {

    protected FlowableEvent event;

    public DispatchEventCommand(FlowableEvent event) {
        this.event = event;
    }

    @Override
    public Void execute(CommandContext commandContext) {
        if (event == null) {
            throw new FlowableIllegalArgumentException("event is null");
        }

        ProcessEngineConfigurationImpl processEngineConfiguration = CommandContextUtil.getProcessEngineConfiguration(commandContext);
        FlowableEventDispatcher eventDispatcher = processEngineConfiguration.getEventDispatcher();
        if (eventDispatcher != null && eventDispatcher.isEnabled()) {
            eventDispatcher.dispatchEvent(event, processEngineConfiguration.getEngineCfgKey());
        } else {
            throw new FlowableException("Message dispatcher is disabled, cannot dispatch " + event);
        }

        return null;
    }

}

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Construct a valid FlowableEvent (e.g. via FlowableEventBuilder) before dispatching.
2. Null-check the event at the call site and handle the absent case explicitly.
3. Fix factory/builder methods to throw instead of returning null.
4. If the event comes from a process variable, add a guard task or validation before the dispatch step.

Example fix

// before
runtimeService.dispatchEvent(myEvent); // myEvent is null
// after
if (myEvent == null) {
    throw new IllegalStateException("event required");
}
runtimeService.dispatchEvent(myEvent);

if (event != null) runtimeService.dispatchEvent(event);

if (event instanceof FlowableEvent) { runtimeService.dispatchEvent(event); }

try { rs.dispatchEvent(event); } catch (FlowableIllegalArgumentException e) { log.warn("Null event skipped", e); }

When it happens

Trigger: Calling runtimeService.dispatchEvent(null) orFlowableEventDispatcher-enabled command wrappers passing an event variable that was never constructed.

Common situations: Custom event builders returning null on error paths (e.g. factory method returning null instead of throwing); process variables holding the event being null; reflection/dynamic dispatch building the event object incorrectly.

Related errors

• processInstanceId is null
• processInstanceIds are null
• taskId and taskIds are null
• Entity cannot be null.
• Error retrieving app engine info

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/6b8ab578abb745e8. Report an issue: GitHub.