presto-spi/src/main/java/io/prestosql/spi/block/SingleMapBlock.java/SingleMapBlock/getLoadedBlock
class SingleMapBlock:    @Override
    public Block getLoadedBlock()
    {
        if (mapBlock.getRawKeyBlock() != mapBlock.getRawKeyBlock().getLoadedBlock()) {
            // keyBlock has to be loaded since MapBlock constructs hash table eagerly.
            throw new IllegalStateException();
        }

        Block loadedValueBlock = mapBlock.getRawValueBlock().getLoadedBlock();
        if (loadedValueBlock == mapBlock.getRawValueBlock()) {
            return this;
        }
        return new SingleMapBlock(
                offset,
                positionCount,
                mapBlock);
    }