Controller.php

<?php

use ActionController; // etc..

/**
 * Example controller
 */
class EventController extends ActionController {
    public function invitePeopleFormAction(SearchForm $searchForm = NULL) {
        // check individual properties of $searchForm, e.g. $searchForm->getEvent()
    }
}

Output.txt

#1255082824: Request hash (HMAC) checking failed. The parameter __hmac was invalid or not set, and objects were modified. (More information)

----
Most likely due to a miscalculation caused by the property set in arguments above.

Template.html

<f:link.action action="invitePeopleForm" arguments="{searchForm: '{event: event}'}">
    Invite people
</f:link.action>