Take sure that parseSearchExpression is runned and everything is set up for it.
$input: The search phrase which was input by the user.
function query_parse_search_expression($input) {
if (!isset($this->search_query)) {
$this->parsed = TRUE;
$this->search_query = db_select('search_index', 'i', array(
'target' => 'slave',
))
->extend('Drupal\\search\\ViewsSearchQuery');
$this->search_query
->searchExpression($input, $this->view->base_table);
$this->search_query
->publicParseSearchExpression();
}
}