code: public T addHeaders(Map<String, String> headers) {
  		if(CollectionUtil.isEmpty(headers)) {
  			return (T)this;
  		}
  		
  		for (Entry<String,String> entry : headers.entrySet()) {
  			this.header(entry.getKey(), StrUtil.nullToEmpty(entry.getValue()), false);
  		}
  		return (T)this;
  	}
docs: 新增请求头<br>
  不覆盖原有请求头
  
  @param headers 请求头
  @return this
  @since 4.0.3