code: public String getText() throws InvalidInputException, ProcessingException, IllegalStateException {
      if (messageML == null) {
        throw new IllegalStateException("The message hasn't been parsed yet. "
            + "Please call MessageMLContext.parse() first.");
      }
  
      String presentationML = getPresentationML();
      Element doc = messageMLParser.parseDocument(presentationML);
      return doc.getTextContent();
    }
docs: Retrieve a string representation of the message by getting the values of
  its PresentationML elements.
  This method returns {@link Element#getTextContent()} of the top-level document tree.
  @throws IllegalStateException thrown if the message hasn't been parsed yet