code: protected String toSignMessageURI(String uri) {
      LoaEnum loa = LoaEnum.parse(uri);
      if (loa == null) {
        return null;
      }
      if (loa.isSignatureMessageUri()) {
        return uri;
      }
      for (LoaEnum l : LoaEnum.values()) {
        if (l.getBaseUri().equals(loa.getBaseUri()) && l.isSignatureMessageUri() && l.isNotified() == loa.isNotified()) {
          return l.getUri();
        }
      }
      return null;
    }
docs: Given a base URI, the method returns its corresponding sigmessage URI.
  
  @param uri
  the URI to transform
  @return the sigmessage URI, or {@code null} if no such exists