code: public static Promise<Long> size(Executor executor, Path path) {
  		return Promise.ofBlockingCallable(executor, () -> Files.isRegularFile(path) ? Files.size(path) : null);
  	}
docs: Checks the file size. For non-regular or non-existing files returns <code>null</code>.
  
  @param executor executor for running tasks in another thread
  @param path     the path of the file to check
  @return file size if given path is a regular file and <code>null</code> if it is a directory or it does not exist