getSingleResult behaviour mismatch for count() and sum() whe

[sventura]

Is is normal that

Number num
 = (Number)entityManager.createQuery(
 "select count(*) from X x;")
 .getSingleResult();

works ok, and

Number num
 = (Number)entityManager.createQuery(
 "select sum(x.id) from X x")
 .getSingleResult();

throws EntityNotFoundException when X has no entities at all?

I expected (since both functions are agregated) none will rice an exception and just return zero.

@Manifest
Too sorry in advance if this is documented else where.

[sventura]

TITLE IS : getSingleResult behaviour mismatch for count() and sum() when no entities found

and I am using 4.0.2 + EJB3RC2 on gentoo with sun-jdk-1.5.05 on postgresql 8.0.3