I don’t know what your actual problem is, but when I use your code of MyType, set it to public and change the code of the disassemble method from

@Override
public Serializable disassemble(MyId value) {
    return value.text;
}

to

@Override
public Serializable disassemble(MyId value) {
    return value;
}

it works in my test case.

If I don’t do this adjustment I get a CIRCULAR REFERENCE: java.lang.ClassCastException.

If there are other problems it would be interesting for me to know about them in order to decide whether we can use this EnhancedUserType.