code: @Nonnull
    public static FileIOError createDirRecursiveIfNotExisting (@Nonnull final Path aDir)
    {
      final FileIOError aError = createDirRecursive (aDir);
      if (aError.getErrorCode ().equals (EFileIOErrorCode.TARGET_ALREADY_EXISTS))
        return aError.withoutErrorCode ();
      return aError;
    }
docs: Create a new directory if it does not exist. The direct parent directory
  already needs to exist.
  
  @param aDir
  The directory to be created if it does not exist. May not be
  <code>null</code>.
  @return A non-<code>null</code> error code.
  @see #createDirRecursive(Path)