getInboundGroupSession method
Implementation
SessionKey? getInboundGroupSession(String roomId, String sessionId) {
  final sess = _inboundGroupSessions[roomId]?[sessionId];
  if (sess != null) {
    if (sess.sessionId != sessionId && sess.sessionId.isNotEmpty) {
      return null;
    }
    return sess;
  }
  return null;
}