code: private void doAppendLine(final String... fields) throws IOException {
  		if (null != fields) {
  			for (int i = 0; i < fields.length; i++) {
  				appendField(fields[i]);
  			}
  			writer.write(config.lineDelimiter);
  			newline = true;
  		}
  	}
docs: 追加一行，末尾会自动换行，但是追加前不会换行
  
  @param fields 字段列表 ({@code null} 值会被做为空值追加)
  @throws IOException IO异常