code: public String getString(String key) {
          return resolver.getMessage(caller, null, ivBundleName, key, null, null, false, null, false);
      }
docs: Retrieve the localized text corresponding to the specified key from the
  ResourceBundle that this instance wrappers. If the text cannot be found
  for any reason, an appropriate error message is returned instead.
  <p>
  
  @param key
  the key to use in the ResourceBundle lookup. Null is
  tolerated.
  @return the appropriate non-null message.