code: public static File getAbsoluteFile(AbstractConfig config, String key) {
      Preconditions.checkNotNull(config, "config cannot be null");
      String path = config.getString(key);
      File file = new File(path);
      if (!file.isAbsolute()) {
        throw new ConfigException(
            key,
            path,
            "Must be an absolute path."
        );
      }
      return new File(path);
    }
docs: Method is used to return a File checking to ensure that it is an absolute path.
  
  @param config config to read the value from
  @param key    key for the value
  @return File for the config value.