code: @NullSafe
    public static File assertExists(File path) throws FileNotFoundException {
      if (isExisting(path)) {
        return path;
      }
  
      throw new FileNotFoundException(String.format("[%1$s] was not found", path));
    }
docs: Asserts that the given file exists.
  
  @param path the {@link File} to assert for existence.
  @return a reference back to the file.
  @throws java.io.FileNotFoundException if the file does not exist.
  @see #isExisting(File)