While executing a query with a simple collection function (e.g. size(), elements()), a wrong warning HHH90000016 is writting to the log.
The syntax of the query is according to the documentation (http://docs.jboss.org/hibernate/orm/5.2/userguide/html_single/Hibernate_User_Guide.html#hql-collection-expressions), e.g. "from persongroup where size(persons) = 0"

In correctly defined queries no warning is expected.

See sample code.