ProxyClient. mapBlocks called in preInit.

public static void mapBlocks() {
        ModelLoader.setCustomStateMapper(RoWTracks.blockTrackStraight, tracksMapper);
    }

    public static StateMapperBase tracksMapper = new StateMapperBase() {
        @Override
        protected ModelResourceLocation getModelResourceLocation(IBlockState iBlockState) {
            if (iBlockState.getBlock() instanceof BlockTrackBase)
                return ModelTrackStraight.modelResourceLocation;
            else
                return null;
        }
    };