How to handle the exception when some field is missing in the JSON input in OIC?

Summary

How can we do schema validation in OIC?

Content

How can we do schema validation in OIC?

we are using xpath in assign variable in OIC for particular fields as shown below

$PO_Date_GET/nssrcmpr:executeResponse/nsmpr9:response-wrapper/nsmpr9:IntegrationEntities/nsmpr9:integrationEntity/nsmpr9:integrationEntityDetails/nsmpr9:poDetails/nsmpr9:items/nsmpr9:item[number(1)]/nsmpr9:referenceRequisitionNo

so if any field is missing it throws an exception like this

in copy assign activity is invalid. There is an user error that results in missing element value(s) in the xpath query. Please review the payload and modeling to ensure that all elements defined in the <from> xpath query have valid non-null values .