def _maybe_visit_value_node(self, value_node: ValueNode):
    """Visit a value node if not cached, and return a corresponding value.

    Args:
      value_node: A `ValueNode`.

    Returns:
      A value corresponding to `value_node` determined by the implementation of
          the abstract `visit` method.
    """
    if value_node not in self._cached_value_nodes_values:
      self._visit_operation(value_node.parent_operation)
    return self._cached_value_nodes_values[value_node]
Visit a value node if not cached, and return a corresponding value.

    Args:
      value_node: A `ValueNode`.

    Returns:
      A value corresponding to `value_node` determined by the implementation of
          the abstract `visit` method.
    
tensorflow_transform/nodes.py