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

        Block loadedValueBlock = valueBlock.getLoadedBlock();
        if (loadedValueBlock == valueBlock) {
            return this;
        }
        return createMapBlockInternal(
                getMapType(),
                startOffset,
                positionCount,
                Optional.ofNullable(mapIsNull),
                offsets,
                keyBlock,
                loadedValueBlock,
                hashTables);
    }