Ошибка PHP warning: array_flip() expects parameter

// Setting values for frontend javascript
$config = array(
	'cssUrl' => $mSearch2->config['cssUrl'].'web/',
	'jsUrl' => $mSearch2->config['jsUrl'].'web/',
	'actionUrl' => $mSearch2->config['actionUrl'],
	'queryVar' => $mSearch2->config['queryVar'],
	'filter_delimeter' => $mSearch2->config['filter_delimeter'],
	'method_delimeter' => $mSearch2->config['method_delimeter'],
	'values_delimeter' => $mSearch2->config['values_delimeter'],
	'start_sort' => $start_sort,
	'start_limit' => $start_limit,
	'start_page' => 1,
	'start_tpl' => '',
	'sort' => $sort == $start_sort ? '' : $sort,
	'limit' => $limit == $start_limit ? '' : $limit,
	'page' => $page,
	'tpl' => !empty($paginatorProperties['tpl_idx'])
			? $paginatorProperties['tpl_idx']
			: '',
	'parentsVar' => $parentsVar,
	'key' => $hash,
	'pageId' => !empty($pageId) ? (integer) $pageId : $modx->resource->id,
	$queryVar => isset($_REQUEST[$queryVar]) ? $_REQUEST[$queryVar] : '',
	$parentsVar => isset($_REQUEST[$parentsVar]) ? $_REQUEST[$parentsVar] : '',
	'aliases' => array_flip($mSearch2->aliases), // строчка №474
);