Why the REST API is ignoring attributes with null values in the JSON Response?

Issue

We have to upgrade JBoss EAP 6.1 to EAP 7.2.0 and RestEasy version from 1.2.1 GA to 3.6.1, and JAXRS 2.1. We observed that the RES API responses ignore attributes with a null value and return only with the attributes which are not null in the JSON response post-migration. We are expecting to return all the attributes (null and Not_null) in the JSON response.