MapDataBridgeMixin.java

@Mixin(net.minecraft.world.storage.MapData.class)
public class MapDataBridgeMixin implements MapDataBridge {
    @Shadow public byte dimension;
    private static Field mapDataBridgeMixin$dimensionId;

    static {
        try {
            if (SpongeImplHooks.isDeobfuscatedEnvironment()) {
                mapDataBridgeMixin$dimensionId = MapData.class.getDeclaredField("dimension");
            } else {
                mapDataBridgeMixin$dimensionId = MapData.class.getDeclaredField("field_76200_c");
            }
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
    }

    @Override
    public int bridge$getDimensionId() {
        try {
            return (int)mapDataBridgeMixin$dimensionId.get(this);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
            return 0;
        }
    }

    @Override
    public void bridge$setDimensionId(int dimensionId) {
        try {
            mapDataBridgeMixin$dimensionId.set(this, dimensionId);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}