Encounter the same problem in 5.3.7 which are described at :

• https://hibernate.atlassian.net/browse/JPA-31
• https://hibernate.atlassian.net/browse/HHH-9165

Refer to the test-case at https://github.com/hibernate/hibernate-orm/commit/c354b5e8b9e157d46c08d3070de5d654e4e6cf11. Changing to use the native SQL

select * from Event where (:name is null or name = :name)

It will then thrown :

Caused by: org.postgresql.util.PSQLException: ERROR: operator does not exist: character varying = bytea
  Hint: No operator matches the given name and argument type(s). You might need to add explicit type casts.

Change to use Hibernate specific API does not have such problem.