protected void publishEvent(Object event) {
        if (this.eventBus != null) {
            this.eventBus.publish(event);
        }
    }
Publishes events on the event bus if the event bus is non-null, otherwise does nothing.

@param event the event to publish on the event bus if the event bus exists.
@since 1.3
core/src/main/java/org/apache/shiro/session/mgt/AbstractNativeSessionManager.java