code: public void prependKeyToDataPath(String key) {
      if (dataPath == null) {
        dataPath = key;
      } else {
        dataPath = key + ((dataPath.charAt(0) == '[') ? "" : ".") + dataPath;
      }
    }
docs: Prepends a key to the data path where this error occurred. E.g. if the dataPath was previously
  'foo.goo' and the key to prepend is 'boo', then the new data path will be 'boo.foo.goo'.
  
  @param key The key to prepend.