Cannot invoke "com.jcraft.jsch.Cipher.isCBC()" because "cipher" is null

[hons82]

Currently I'm not able to reproduce this issue, but we got the following stacktrace in our logs sometimes

Cannot invoke "com.jcraft.jsch.Cipher.isCBC()" because "cipher" is null
	java.lang.NullPointerException: Cannot invoke "com.jcraft.jsch.Cipher.isCBC()" because "cipher" is null
		at com.jcraft.jsch.Session.start_discard(Session.java:1420)
		at com.jcraft.jsch.Session.read(Session.java:1240)
		at com.jcraft.jsch.Session.connect(Session.java:326)

The connect method is called by our code which is more or less this:

 public boolean isConnected() {
  return session != null && session.isConnected();
 }

 public synchronized boolean connect(int port) {
  try {
   if (!isConnected()) {
    JSch jsch = new JSch();
    KeyPair kp = getTunnelKeyPair();
    if (kp != null) {
     jsch.addIdentity(username, toByteArray(kp.getPrivate()), null, null);
    }
    session = jsch.getSession(username, "localhost", port);
    session.setServerAliveInterval(45000);
    session.setConfig("StrictHostKeyChecking", "no");
    session.connect(CONNECTION_TIMEOUT);
   }
  }
  catch (JSchException | IOException e) {
   LOGGER.log(Debug.INFO, "SSH connect", e.getMessage());
   disconnect();
  }
  return isConnected();
 }

 public synchronized void disconnect() {
  if (session != null)
   session.disconnect();
 }
 

Is there a way that I can check if this chiper exists prior to call connect, to avoid running into this Nullpointer?