on</span><span>(</span><span class="phpdocumentor-signature__argument"><span class="phpdocumentor-signature__argument__return-type"><a href="classes/LINE-Clients-MessagingApi-Model-Action.html"><abbr title="\LINE\Clients\MessagingApi\Model\Action">Action</abbr></a>|null&nbsp;</span><span class="phpdocumentor-signature__argument__name">$action</span></span><span>)</span><span> : </span><span class="phpdocumentor-signature__response_type">self</span></code>

    
        <h5 class="phpdocumentor-argument-list