code: @Nonnull
    public static FileIOError createDirIfNotExisting (@Nonnull final File aDir)
    {
      final FileIOError aError = createDir (aDir);
      if (aError.getErrorCode ().equals (EFileIOErrorCode.TARGET_ALREADY_EXISTS))
        return EFileIOErrorCode.NO_ERROR.getAsIOError (EFileIOOperation.CREATE_DIR, aDir);
      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.