code: private final String internalGetMessage(String key) {
          if(getResourceBundlePath() == null)
              return getDefaultMessage(key);
          else {
              /* ensure that the correct resource bundles are created */
              if(_resourceBundle == null) {
                  _resourceBundle = createResourceBundle(getResourceBundlePath());
              }
  
              if(isEnableChaining() && _resourceBundleKeys == null) {
                  Enumeration e = _resourceBundle.getKeys();
                  while(e.hasMoreElements())
                      _resourceBundleKeys.put(e.nextElement(), VALUE_PLACEHOLDER);
              }
  
              if(!isEnableChaining() || _resourceBundleKeys.containsKey(key))
                  return _resourceBundle.getString(key);
              else
                  return _defaultResourceBundle.getString(key);
          }
      }
docs: Lookup a message given a message key.  If chaining is enabled via
  {@link DataGridResourceProvider#setEnableChaining(boolean)}, the outer resource bundle will be searched,
  first.  If no message matching the message key is found, the default resource bundle is searched.
  @param key the key
  @return the message.