code: 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;
      }
docs: Add an additional HTTP header passed to the proxy server.
  
  @param name
  The name of an HTTP header (case-insensitive).
  If {@code null} or an empty string is given,
  nothing is added.
  
  @param value
  The value of the HTTP header.
  
  @return
  {@code this} object.