public function all($project_id = null, $page = 1, $per_page = self::PER_PAGE, array $params = array())
{
$path = $project_id === null ? 'issues' : $this->getProjectPath($project_id, 'issues');
$params = array_intersect_key($params, array('labels' => '', 'state' => '', 'sort' => '', 'order_by' => '', 'milestone' => ''));
$params = array_merge(array('page' => $page, 'per_page' => $per_page), $params);
return $this->get($path, $params);
}