public void add(final String name, final String value) {
    List<String> values = headers.get(name);
    if (values == null) {
      set(name, value);
    } else {
      values.add(value);
    }
  }
Add a header name/value mapping. Add the specified value to the list of
values associated to the specified header name.

@param name
         the header name.
@param value
         the header value.
crawler-commons/src/main/java/achecrawler/crawler/crawlercommons/util/Headers.java