presto-rcfile/src/main/java/io/prestosql/rcfile/text/BinaryEncoding.java/BinaryEncoding/decodeColumn
class BinaryEncoding:    @Override
    public Block decodeColumn(ColumnData columnData)
    {
        int size = columnData.rowCount();
        BlockBuilder builder = type.createBlockBuilder(null, size);

        Slice slice = columnData.getSlice();
        for (int i = 0; i < size; i++) {
            int offset = columnData.getOffset(i);
            int length = columnData.getLength(i);
            if (nullSequence.equals(0, nullSequence.length(), slice, offset, length)) {
                builder.appendNull();
            }
            else {
                byte[] data = slice.getBytes(offset, length);
                type.writeSlice(builder, Slices.wrappedBuffer(base64Decoder.decode(data)));
            }
        }
        return builder.build();
    }