docs: @Pure
  	public static File removeExtension(File filename) {
  		if (filename == null) {
  			return null;
  		}
  		final File dir = filename.getParentFile();
  		final String name = filename.getName();
  		final int idx = name.lastIndexOf(getFileExtensionCharacter());
  		if (idx < 0) {
  			return filename;
  		}
  		return new File(dir, name.substring(0, idx));
  	}