public function __construct(Application $application, CompletionContext $context = null)
{
$this->application = $application;
$this->context = $context;
$this->addHandler(new Completion('help', 'command_name', Completion::TYPE_ARGUMENT, array_keys($application->all())));
$this->addHandler(new Completion('list', 'namespace', Completion::TYPE_ARGUMENT, $application->getNamespaces()));
}