docs: public static byte[] toByte(Set<MetaData> metadataSet, Charset charset) {
          if (null == metadataSet || metadataSet.isEmpty()) {
              return new byte[0];
          }
          StringBuilder sb = new StringBuilder(32 * metadataSet.size());
          for (MetaData md : metadataSet) {
              sb.append(md.getName()).append(OtherConstants.FDFS_FIELD_SEPERATOR).append(md.getValue());
              sb.append(OtherConstants.FDFS_RECORD_SEPERATOR);
          }
          // 去除最后一个分隔符
          sb.delete(sb.length() - OtherConstants.FDFS_RECORD_SEPERATOR.length(), sb.length());
          return sb.toString().getBytes(charset);
      }