code: @Nonnull
    @ReturnsMutableCopy
    public static ICommonsList <File> getDirectoryContent (@Nonnull final File aDirectory)
    {
      ValueEnforcer.notNull (aDirectory, "Directory");
  
      return _getDirectoryContent (aDirectory, aDirectory.listFiles ());
    }
docs: This is a replacement for <code>File.listFiles()</code> doing some
  additional checks on permissions. The order of the returned files is
  defined by the underlying {@link File#listFiles()} method.
  
  @param aDirectory
  The directory to be listed. May not be <code>null</code>.
  @return Never <code>null</code>.