docs: def _pop_input_state(self, node):
          """
          Get the input abstract state for this node, and remove it from the state map.
  
          :param node: The node in graph.
          :return:     A merged state, or None if there is no input state for this node available.
          """
  
          if node in self._state_map:
              return self._state_map.pop(node)
          return None