code: @Override
  	public void set(String headerName, String headerValue) {
  		List<String> headerValues = new LinkedList<String>();
  		headerValues.add(headerValue);
  		headers.put(headerName, headerValues);
  	}
docs: Set the given, single header value under the given name.
  @param headerName the header name
  @param headerValue the header value
  @throws UnsupportedOperationException if adding headers is not supported
  @see #put(String, List)
  @see #add(String, String)