docs: public ProxySettings addHeader(String name, String value)
      {
          if (name == null || name.length() == 0)
          {
              return this;
          }
  
          List<String> list = mHeaders.get(name);
  
          if (list == null)
          {
              list = new ArrayList<String>();
              mHeaders.put(name, list);
          }
  
          list.add(value);
  
          return this;
      }