code: public String getString(String key, String defaultString) {
          if (key == null) {
              return defaultString;
          }
          try {
              String result = getString(key);
              return result;
          } catch (MissingResourceException e) {
              return defaultString;
          }
      }
docs: Overrides ResourceBundle.getString. Adds some error checking to ensure that
  we got a non-null key and resource bundle.
  
  Adds default string functionality. If the key for the resource
  was not found, return the default string passed in. This way
  something displays, even if it is in English.
  
  @param key Name portion of "name=value" pair.
  @param defaultString String to return if the key was null, or if
  resource was not found
  (MissingResourceException thrown).