WordPress All in One Event Calendar - Override Avatar

ai1ec_override_avatar.php

<?php
//Place in mu-plugins folder
//Custom Twig Template Functions

function opubco_add_twig_functions_and_filters( $registry ) {
  $loader = $registry->get('theme.loader');
  $twig = $loader->get_twig_instance(false, true);
  $twig->addFunction( new Twig_SimpleFunction('opubco_get_event_avatar', 'opubco_get_event_avatar') );
}
add_action( 'ai1ec_loaded', 'opubco_add_twig_functions_and_filters');

//$post_id of the event
function opubco_get_event_avatar( $post_id, $size ) {
	if ( has_post_thumbnail( $post_id ) ) {
		return get_the_post_thumbnail( $post_id, $size );
	} else {
		return '';
	}
}

{{ opubco_get_event_avatar( event.post_id, 'event_thumb' ) | raw }}