code: public BoardingPassBuilder addBoardingPass(String passengerName,
  			String pnrNumber, String logoImageUrl, String aboveBarCodeImageUrl) {
  		return new BoardingPassBuilder(this, passengerName, pnrNumber,
  				logoImageUrl, aboveBarCodeImageUrl);
  	}
docs: Adds a {@link BoardingPass} object to this template. This field is
  mandatory for this template and should contain at least one element.
  
  @param passengerName
  the passenger name. It can't be empty.
  @param pnrNumber
  the Passenger Name Record number (Booking Number). It can't be
  empty.
  @param logoImageUrl
  the URL of the logo. It can't be empty.
  @param aboveBarCodeImageUrl
  the URL of the image to be shown above the bar code in the
  center of the pass. It can't be empty.
  @return a builder for a {@link BoardingPass} object.