public function pullRequests(string $user, string $repo, array $filter = []): array
    {
        $default = [];
        $api = $this->client->api('pull_request');
        $params = [$user, $repo, $filter];

        $refs = $this->callGitHub([$api, 'all'], $params, $default);

        usort($refs, $this->prSorter($user));

        return $refs;
    }