code: public WriterFlushResult withFlushResult(WriterFlushResult flushResult) {
          this.flushedBytes.addAndGet(flushResult.flushedBytes.get());
          this.mergedBytes.addAndGet(flushResult.mergedBytes.get());
          this.flushedAttributes.addAndGet(flushResult.flushedAttributes.get());
          return this;
      }
docs: Adds the given WriterFlushResult to this one.
  
  @param flushResult The flush result to add.
  @return This object.