Okay I found the issue( HHH-5946 Closed ) that I was looking for but it wasn't exactly about nulls but more about equality in general.
Could you still try with hibernate 5 too and maybe even upload a running testcase based on this template?
@steve is this expected behavior? I haven't encountered that yet because I don't do embeddable comparisons, but sounds like a serious bug that is not so easy to fix because it alters the sql query based on the parameter values or requires some more complex expressions to be generated.

I dug a bit into the topic and there actually is an operator in SQL99 for this called IS DISTINCT FROM which does exactly what we want, but it's only supported by a handful of dbms and the workaround gets quite complex.
Here some links

• http://stackoverflow.com/questions/10416789/how-to-rewrite-is-distinct-from-and-is-not-distinct-from
• https://blog.jooq.org/2012/09/21/the-is-distinct-from-predicate/
• https://www.ibm.com/support/knowledgecenter/SSEPEK_10.0.0/com.ibm.db2z10.doc.sqlref/src/tpc/db2z_distinctpredicate.html
• https://wiki.postgresql.org/wiki/Is_distinct_from
• http://www.firebirdsql.org/refdocs/langrefupd20-distinct.html
• http://www.h2database.com/html/grammar.html#condition_right_hand_side
• http://hsqldb.org/doc/guide/dataaccess-chapt.html#dac_sql_predicates