Need help removing an error.

Hello,
I have the plugin working great most of the time. On certain searches I get the following error message on the top of the screen – sometimes 10-15 times the same message.
Warning: array_push() expects parameter 1 to be array, null given in …/functions.php on line 177

I don’t know php, and would be grateful if someone could help me fix this error.

/* Relevanssi Products First! */
add_filter(‘relevanssi_hits_filter’, ‘products_first’);
function products_first($hits) {
$types = array();

$types[‘page’] = array();
$types[‘post’] = array();
$types[‘product’] = array();
$types[‘x-portfolio’] = array();

// Split the post types in array $types
if (!empty($hits)) {
foreach ($hits[0] as $hit) {
[this is line 177] array_push($types[$hit->post_type], $hit);
}
}

// Merge back to $hits in the desired order
$hits[0] = array_merge($types[‘product’], $types[‘post’], $types[‘page’], $types[‘x-portfolio’]);
return $hits;
}

https://wordpress.org/plugins/relevanssi/