com.esotericsoftware.kryo.KryoException: java.lang.UnsupportedOperationException: java.io.StringReader, which is a closeable resource

I have a Intiator and a responder flow in my corda project.
I am sending a stringified json in my Initiator flow and expecting a string as acknowledgement from counterparty.

String acknowledgment = 
counterPartySession.sendAndReceive(String.class,jsonMessage.toString()).unwrap(data -> data);

And in the counter party flow I am trying to retrieve the message and send a string as response.

JSONParser parser = new JSONParser();
String receivedMessage = session.receive(String.class).unwrap(data -> data);
JSONObject jsonObject = (JSONObject) parser.parse(receivedMessage);
String correlationId = (String) jsonObject.get("correlationId");
String response = "received message with correlationId: "+correlationId;
session.send(response);

but In the counter party flow I am getting an error with below stack trace.

com.esotericsoftware.kryo.KryoException: java.lang.UnsupportedOperationException: java.io.StringReader, which is a closeable resource, has been detected during flow checkpointing. Restoring such resources across node restarts is not supported. Make sure code accessing it is confined to a private method or the reference is nulled out.
Serialization trace:
zzReader (org.json.simple.parser.Yylex)
lexer (org.json.simple.parser.JSONParser)
dataObject (co.paralleluniverse.fibers.Stack)
stack (net.corda.node.services.statemachine.FlowStateMachineImpl)
	at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:101) ~[kryo-4.0.2.jar:?]
	at com.esotericsoftware.kryo.serializers.CompatibleFieldSerializer.write(CompatibleFieldSerializer.java:65) ~[kryo-4.0.2.jar:?]
	at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:575) ~[kryo-4.0.2.jar:?]
	at co.paralleluniverse.io.serialization.kryo.ReplaceableObjectKryo.writeObject(ReplaceableObjectKryo.java:85) ~[quasar-core-0.7.10-jdk8.jar:0.7.10]
	at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:79) ~[kryo-4.0.2.jar:?]
	at com.esotericsoftware.kryo.serializers.CompatibleFieldSerializer.write(CompatibleFieldSerializer.java:65) ~[kryo-4.0.2.jar:?]
	at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:575) ~[kryo-4.0.2.jar:?]
	at co.paralleluniverse.io.serialization.kryo.ReplaceableObjectKryo.writeClassAndObject(ReplaceableObjectKryo.java:54) ~[quasar-core-0.7.10-jdk8.jar:0.7.10]
	at com.esotericsoftware.kryo.serializers.DefaultArraySerializers$ObjectArraySerializer.write(DefaultArraySerializers.java:361) ~[kryo-4.0.2.jar:?]

When a flow checkpoints, it serializes the current execution stack.

The error says java.io.StringReader, cannot be serialized since it is closable. You should put the piece of code in a separate method, that is not annotated with @Suspendable or a better way would be to put it inside a CordaService.