Get preview for URL.

        Args:
            url (str): URL to get a preview
            ts (double): The preferred point in time to return
                 a preview for. The server may return a newer
                 version if it does not have the requested
                 version available.

def get_url_preview(self, url, ts=None):
        """Get preview for URL.

        Args:
            url (str): URL to get a preview
            ts (double): The preferred point in time to return
                 a preview for. The server may return a newer
                 version if it does not have the requested
                 version available.
        """
        params = {'url': url}
        if ts:
            params['ts'] = ts
        return self._send(
            "GET", "",
            query_params=params,
            api_path="/_matrix/media/r0/preview_url"
        )