code: public static Gson createH2oCompatibleGson() {
      return new GsonBuilder()
              // .registerTypeAdapterFactory(new ModelV3TypeAdapter())
              .registerTypeAdapter(KeyV3.class, new KeySerializer())
              .registerTypeAdapter(FrameV3.ColSpecifierV3.class, new ColSerializer())
              // .registerTypeAdapter(ModelBuilderSchema.class, new ModelDeserializer())
              // .registerTypeAdapter(ModelSchemaBaseV3.class, new ModelSchemaDeserializer())
              .create();
    }
docs: Create a Gson JSON serializer / deserializer that has custom handling for certain H2O classes for
  which our REST API does automagic type conversions.
  <p>
  TODO: this method is copy-pasted from H2oApi.java in a more limited form; refactor.
  See the comments there.