code: def _ParseExtensionsString(self, extensions_string):
      
      if not extensions_string:
        return
  
      extensions_string = extensions_string.lower()
      extensions = [
          extension.strip() for extension in extensions_string.split(',')]
      file_entry_filter = file_entry_filters.ExtensionsFileEntryFilter(extensions)
      self._filter_collection.AddFilter(file_entry_filter)
docs: Parses the extensions string.
  
      Args:
        extensions_string (str): comma separated extensions to filter.