We will be adding some improvements to this for 6.0. JPA's converter stuff is like most things coming from a spec... good for general cases, but severely limiting for anything non-trivial: especially to the providers.

The warning is really an indication that Hibernate knows nothing about the semantic of the indicated type (com.example.SomeClass) and is going to make some assumptions. The assumptions need to be safe for all cases, which means they are not necessarily the best choices in all cases. So the improvements we have in mind are around being able to supply the semantic information about these Java types. The biggest one is "mutability" which has implications in terms of making deep copies and knowing how "deeply" to check for equality.

In the short term, the easiest solution if you find this to be a problem is to register the JavaTypeDescriptor that defines the "semantic information" about a given Java type. IIRC however that ability was not added until 5.0. It may or may not be there in 4.3. 4.3 is way past support, so I am not sure anymore. If you are interested in exploring this option, look for JavaTypeDescriptorRegistry. It is available statically (an unfortunate design design we will also address in 6.0) via {{JavaTypeDescriptorRegistry#INSTANCE}.