Why is the reducer not updating the state?

Question

React

component code:

setDefaultParams() {
    store.dispatch({

      type: 'UPDATE_CHANGED',
      payload: merge({}, this.state.changed, this.props._sharedData.request)

    });
  }

filterActions reducer:

export default function ( state = null, action){

  switch( action.type ){

    case "UPDATE_CHANGED" :

      return Object.assign({}, state, { filterParams : action.payload });


    default : return state;
  }

}

and CombineReducer:

import { combineReducers } from 'redux';

import filterParams from './filters/filterParams';

import filterActions from './filters/filterActions';


export default combineReducers({
  filterParams,
  filterActions
})