code: def default_index(func):
      
  
      @wraps(func)
      def check_default_index(self, *args, **kwargs):
          if self._file_path != self._index_path():
              raise AssertionError(
                  "Cannot call %r on indices that do not represent the default git index" % func.__name__)
          return func(self, *args, **kwargs)
      # END wrapper method
  
      return check_default_index
docs: Decorator assuring the wrapped method may only run if we are the default
      repository index. This is as we rely on git commands that operate
      on that index only.