fail.on.missing.attribute is not working with the default source mapper

[HasithaAthukorala]

Description:
Tried with the below source mapper. I have used fail.on.missing.attribute as false, but it fails when an attribute is missing.

@source(type="runtime-agent", port="9411", @Map(type="json", fail.on.missing.attribute="false"))
define stream ZipkinStreamIn(traceId string, id string, parentId string, operationName string, serviceName string, spanKind string, timestamp long, duration long, tags string);

received error : not in an accepted format for default mapping. Hence dropping the message.

Affected Siddhi Version: 4.1.38

[niveathika]

This is related to https://github.com/siddhi-io/siddhi-map-json and should be moved.