code: def persist(self) -> None:
      if self._mapping != self._initial_mapping:
          self._state.clear()
          for window_for_user, window_in_state in self._mapping.items():
              self._state.put(window_for_user, window_in_state)
  
file_path: flink/flink-python/pyflink/fn_execution/datastream/window/merging_window_set.py
imports: from abc import ABC, abstractmethod
  from typing import TypeVar, Generic, Collection, Iterable
  from pyflink.datastream import MergingWindowAssigner
  from pyflink.datastream.state import MapState
label_desc: Use image node_id 2 for calling the MergingWindowSet obj's underlying member method code with example usage: obj.persist() without return types