public static void override(List<FileSystemInterface> overrideExtensionList){
  if (overrideExtensionList != null) {
    extensionList=overrideExtensionList;
  }
 else {
    extensionList.clear();
  }
}

public static void override ( List < FileSystemInterface > overrideExtensionList ) { if ( overrideExtensionList != null ) { extensionList = overrideExtensionList ; } else { extensionList . clear ( ) ; } }
allows list of file extensions to be overridden .
