Invalid json string error thrown in JsonSinkMapper

[dilini-muthumala]

Description: The JSON sink mapper thorws the followng error when tryong to create a nested json format.

ERROR {io.siddhi.extension.map.json.sinkmapper.JsonSinkMapper} - Invalid json string : {"event":{"alertTypeData":{"PublisherName":"ee","AlertCategory":"rr","AlertType":"rr"},"recipientData":{"recipientType":"rr"}. Hence dropping the message.

Affected Product Version: wso2si-4.0.0, wso2si-tooling-4.0.0

OS, DB, other environment details and versions: N/A

Steps to reproduce:

@App:name("PreDefinedProducerApp") 
@App:description("PreDefined Local Kafka Producer App")
define stream DataStream(PublisherName string,AlertCategory String,AlertType String,recipientType String);
@sink(type='log', 
@map(type='json', enclosing.element='event', validate.json='true', @payload("""{"alertTypeData":{"PublisherName":"{{PublisherName}}","AlertCategory":"{{AlertCategory}}","AlertType":"{{AlertType}}"},"recipientData":{"recipientType":"{{recipientType}}"}}""")))
define stream DataWriteStream (PublisherName string, AlertCategory string, AlertType string, recipientType string);
from DataStream
select PublisherName, AlertCategory, AlertType , recipientType
insert into DataWriteStream;

Related Issues: https://github.com/wso2/product-sp/issues/1075