public function store(
        $account_id = null,
        $identifier = null,
        $username = null,
        $address,
        $verified = null,
        $upstream_app_name = null,
        $verification_callback = null,
        $confirmation_from = null
    )
    {
        $fields = [];
        //@todo validate params, throw exception when they are missing
        if (!is_null($account_id)) $fields['account_id'] = $account_id;
        if (!is_null($identifier)) $fields['identifier'] = $identifier;
        if (!is_null($username)) $fields['username'] = $username;
        $fields['address'] = $address;
        if (!is_null($verified)) $fields['verified'] = $verified;
        if (!is_null($upstream_app_name)) $fields['upstream_app_name'] = $upstream_app_name;
        if (!is_null($verification_callback)) $fields['verification_callback'] = $verification_callback;
        if (!is_null($confirmation_from)) $fields['confirmation_from'] = $confirmation_from;

        return $this->_post($fields);
    }