message: fix(datepicker): if value is null dont reset date to 1970
  fix if state.value == null _newState.value will set to '1970-01-01 08:00:00'
diff: @@ -100,8 +100,10 @@ export function timepickerReducer(state = initialState, action: Action) {
  };
  if (state.config.showMeridian !== _newState.config.showMeridian) {
  + if(state.value){
  _newState.value = new Date(state.value);
  }
  + }
  return Object.assign({}, state, _newState);
  }
  