presto-rcfile/src/main/java/io/prestosql/rcfile/text/BlockEncoding.java/BlockEncoding/decodeColumn
class BlockEncoding:    @Override
    public final Block decodeColumn(ColumnData columnData)
            throws RcFileCorruptionException
    {
        int size = columnData.rowCount();

        Slice slice = columnData.getSlice();
        BlockBuilder builder = type.createBlockBuilder(null, size);
        for (int i = 0; i < size; i++) {
            int length = columnData.getLength(i);
            int offset = columnData.getOffset(i);
            if (!isNullSequence(slice, offset, length)) {
                decodeValueInto(1, builder, slice, offset, length);
            }
            else {
                builder.appendNull();
            }
        }

        return builder.build();
    }