How to correctly transfer objects from client to server via Socket(SocketException: connection reset)?

Question

Java

Good day to all! I practice transferring data over sockets from the client to the server and vice versa, in the case of transferring text through the PrintWriter, everything works fine, but as soon as I try to transfer objects through the ObjectOutputStream, the server throws a SocketException: connection reset.
Essence: the client connects to the server and sends him a message - an object containing the name of the sender and his ID. The server accepts this object and prints the name and ID of the sender to the console.

Server

package objectschange;

import java.io.*;
import java.net.*;

public class ServerSide {

  protected ObjectInputStream serverOIS;
  public static void main(String[] args) {
    ServerSide server = new ServerSide();
    server.launchServer();
  }

  private void launchServer() {
    try {
      ServerSocket srvSocket = new ServerSocket(3200);

      while (true) {
        Socket serverClientSocket = srvSocket.accept();

        serverOIS = new ObjectInputStream(serverClientSocket.getInputStream());
        handleObject(serverOIS);
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }

  private void handleObject(ObjectInputStream serverOIStream) {
    ClientMessagePackage messagePackage;
    try {
      while ((messagePackage = (ClientMessagePackage) serverOIStream.readObject()) != null) {
        System.out.println(messagePackage.packageSender + " " + messagePackage.packageSenderID);
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
}

Customer

package objectschange;

import java.io.*;
import java.net.*;

public class ClientSide  {

  protected ObjectOutputStream clientOOS;

  public static void main(String[] args) {
    ClientSide client = new ClientSide();
    client.establishConnection();
  }

  private void establishConnection() {
    try {
      Socket clientSocket = new Socket("127.0.0.1", 3200);
      Thread.sleep(3000);
      clientOOS = new ObjectOutputStream(clientSocket.getOutputStream());

      sendPackage(clientOOS, new ClientMessagePackage("Name", 1));
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }

  private void sendPackage(ObjectOutputStream clientOOStream, ClientMessagePackage clientMPackage) {
    try {
      clientOOStream.writeObject(clientMPackage);
      clientOOStream.flush();
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }

}

class ClientMessagePackage implements Serializable {

  protected String packageSender;
  protected int packageSenderID;

  protected ClientMessagePackage(String name, int id) {
    packageSender = name;
    packageSenderID = id;
  }
}

I start the server first, waiting for the request, then the client connecting to it. Console:

Console

Moreover, if after the first client we connect another one, then eventually the object with the message reaches the server, it prints it to the console, but then an exception is thrown again:

Console

If I understand correctly, the client disconnects from the server on its own(?), why is this happening?
I can not understand what is the problem, I ask for your advice.
Thanks in advance for your replies!