return null;
}
IChannelPreferences cPrefs = channel.newDefaultPreferences();
IParams fullParams = new Params().setAll(cPrefs.getParams()).setAll(params);
StringBuilder buf = new StringBuilder(_baseUrl);
buf.append(_mountPath).append(_pullPrefix).append(channelId).append("/").append(userId);
buf.append("?");
for (final ParamValue pv : fullParams) {