message: workaround for
  unsure our vector url match could ever return undefined, but apparently it is...
diff: @@ -148,7 +148,7 @@ var sanitizeHtmlParams = {
  attribs.href = m[1];
  delete attribs.target;
  }
  -
  + else {
  m = attribs.href.match(linkifyMatrix.MATRIXTO_URL_PATTERN);
  if (m) {
  var entity = m[1];
  @@ -161,6 +161,7 @@ var sanitizeHtmlParams = {
  delete attribs.target;
  }
  }
  + }
  attribs.rel = 'noopener'; // https://mathiasbynens.github.io/rel-noopener/
  return { tagName: tagName, attribs : attribs };
  },
  