@Override
    public void flush() throws IOException {
        if (!finished) {
            writeBlock();
        }
        if (out != null) {
            out.flush();
        }
    }
Similar to the {@link #writeBlock()} method. Writes a 0-length block (without block checksum) to signal the end
of the block stream.

@throws IOException
clients/src/main/java/org/apache/kafka/common/compress/Lz4BlockOutputStream.java