fix dto.entries repetition errors by improving the api for access to internal fields

not as clean as it could be, but quick and safe, as this is needed in production systems
Personal preference: I'm a big fan of not returning null when an `ImmutableMap.of()` means the same thing. Same for returning an `ImmutableList.of()` from `getUniqueEntries()`. It saves null guards all over the place, and NPEs when someone forgets to guard against null.