After more research, I figured that the classic hibernate configuration that I am using for backwards compatibility on return types of aggregate functions is causing the issue. The classic configuration is as per the hibernate migration document.
https://community.jboss.org/wiki/HibernateCoreMigrationGuide32

Configuration classicCfg = new Configuration();
classicCfg.addSqlFunction( "count", new ClassicCountFunction());
classicCfg.addSqlFunction( "avg", new ClassicAvgFunction());
classicCfg.addSqlFunction( "sum", new ClassicSumFunction());
SessionFactory classicSf = classicCfg.buildSessionFactory();