code: public String getByName(final String name) {
  		if (headerMap == null) {
  			throw new IllegalStateException("No header available");
  		}
  
  		final Integer col = headerMap.get(name);
  		if (col != null) {
  			return get(col);
  		}
  		return null;
  	}
docs: 获取标题对应的字段内容
  
  @param name 标题名
  @return 字段值，null表示无此字段值
  @throws IllegalStateException CSV文件无标题行抛出此异常