@steve

The basis of that seems to be a belief that "the JPA implementation is supposed to add them", which is flat out inaccurate; JPA does not even define support for multi-valued params - that's a Hibernate feature.

In the JPA 2.1 PDF, page 195, section 4.6.17.5 they give this example as a valid query:

SELECT e
FROM Employee e
WHERE TYPE(e) IN :empTypes

They may not have specifically outlined it in the setParameter definition, but collection expansion is expected behaviour.

Sounds like you've thought of it as a bonus feature, when it really should be standard.