public function picker($query, $maxResults = null, $showAvatar = null, $exclude = null)
    {
        $parameters = array(
            'query' => $query,
            'maxResults' => $maxResults,
            'showAvatar' => $showAvatar,
            'exclude' => $exclude
        );
        return $this->apiClient->callEndpoint(sprintf('%s/picker', self::ENDPOINT), $parameters);
    }