presto-hive/src/main/java/io/prestosql/plugin/hive/HivePageSource.java/HivePageSource/CoercionLazyBlockLoader
class HivePageSource:        public CoercionLazyBlockLoader(Block block, Function<Block, Block> coercer)
        {
            this.block = requireNonNull(block, "block is null");
            this.coercer = requireNonNull(coercer, "coercer is null");
        }