code: @OverrideOnDemand
    protected boolean recurseIntoDirectory (@Nonnull final File aDirectory)
    {
      return m_aRecursionFilter == null || m_aRecursionFilter.test (aDirectory);
    }
docs: Override this method to manually filter the directories, which are recursed
  into.
  
  @param aDirectory
  The non-<code>null</code> directory
  @return <code>true</code> if all children of this directory should be
  investigated