How do I modify the error code array used by “shake_error_codes” filter?

OK, my php is a little rusty. Doing a “return” on an array_push does not return the array. So had to change my add_filter to:

add_filter( 'shake_error_codes', 'custom_add_error_code');
function custom_add_error_code($error_code) {
    array_push($error_code, 'gov_email');
    return $error_code;
}