message: Monitoring: Don't allow silence comments to only contain whitespace
  The `textarea`'s `required` attribute catches the case where Comment is
  not provided, so this error message is just for the case where Comment
  is provided by only contains whitespace characters.
diff: @@ -1338,6 +1338,12 @@ const SilenceForm_: React.FC<SilenceFormProps> = ({ defaults, Info, title }) =>
  const onSubmit: React.FormEventHandler<HTMLFormElement> = (e) => {
  e.preventDefault();
  + // Don't allow comments to only contain whitespace
  + if (_.trim(comment) === '') {
  + setError('Comment is required.');
  + return;
  + }
  +
  const { alertManagerBaseURL } = window.SERVER_FLAGS;
  if (!alertManagerBaseURL) {
  setError('Alertmanager URL not set');
  