NullPointerException using non-ANSI function in CriteriaQuery in Hibernate

Issue

• Building a CriteriaQuery using SQL Server function datediff

              CriteriaBuilder cb = entityManager.getCriteriaBuilder();
              CriteriaQuery<Date> cq = cb.createQuery(Date.class);
              Root<Employee> root = cq.from(Employee.class);
              final Expression<BigInteger> diff = cb.function("datediff", BigInteger.class,
                      cb.literal("ms"),
                      root.get(Employee_.hireDate),
                      root.get(Employee_.someDate)
              ).as(BigInteger.class);
              cq.multiselect(diff);
              for (Object o : entityManager.createQuery(cq).getResultList()) {
                      log.info("ActiveTime: " + Date.class.cast(o).getTime());
              }
  

• Encountering the error below

  java.lang.NullPointerException
      at org.hibernate.dialect.function.StandardAnsiSqlAggregationFunctions$SumFunction.determineJdbcTypeCode(StandardAnsiSqlAggregationFunctions.java:200)
      at org.hibernate.dialect.function.StandardAnsiSqlAggregationFunctions$SumFunction.getReturnType(StandardAnsiSqlAggregationFunctions.java:158)
      at org.hibernate.hql.internal.ast.util.SessionFactoryHelper.findFunctionReturnType(SessionFactoryHelper.java:414)
      at org.hibernate.hql.internal.ast.tree.AggregateNode.getDataType(AggregateNode.java:68)
      ...
      at org.hibernate.jpa.criteria.compile.CriteriaCompiler.compile(CriteriaCompiler.java:130)
      at org.hibernate.jpa.spi.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:699)
      ...