The below is from the JPA 2.2 spec, I agree that it is not clearly defined what we must do exactly.

/**
* Find by primary key, using the specified properties.Search for an entity of the specified class and primary key.
* If the entity instance is contained in the persistence context
* it is returned from there.
* If a vendor-specific property or hint is not recognized,
* it is silently ignored.
* @param entityClass
* @param primaryKey
* @param properties standard and vendor-specific properties
* and hints
* @return the found entity instance or null if the entity does
* not exist
* @throws IllegalArgumentException if the first argument does
* not denote an entity type or the second argument is
* is not a valid type for that entity’s primary key or
* is null
*/
public <T> T find(Class<T> entityClass,
Object primaryKey,
Map<String, Object> properties);

I'll check a few more things before responding again:

1. Check the test that I am running, against the JPA 2.1 version of the same test, to see if something changed in the test.
2. Look a bit deeper at the running test case, to see if I can better capture the conditions that cause us to see an exception thrown, instead of null being returned.
3. If I fail to get anything conclusive from #1 + #2, I will push for introducing an IronJacamar option to allow disabling this exception.