docs: public static List<File> findFilesWithFilter(final File dir, final String... extension)
  	{
  		final List<File> foundedFileList = new ArrayList<>();
  		final File[] children = dir.listFiles(new MultiplyExtensionsFileFilter(true, extension));
  		for (final File element : children)
  		{
  			// if the entry is a directory
  			if (element.isDirectory())
  			{ // then
  				// find recursively in the directory and put it in a List.
  				// Put the founded files in the main List.
  				foundedFileList.addAll(findFilesWithFilter(element, extension));
  			}
  			else
  			{
  				foundedFileList.add(element.getAbsoluteFile());
  			}
  		}
  		return foundedFileList;
  	}