Need assistance to fix console error saying ‘Uncaught (in promise)’

i’m trying to solve a problem in which i have to use a find() method and it’s giving me an error

import { CART_ADD_ITEM, CART_REMOVE_ITEM } from '../constants/cartConstant';

const cartReducers = (state = { cartItems: [] }, action) => {
  switch (action.type) {
    case CART_ADD_ITEM:
      const item = action.payload;

      const existItem = state.cartItems.find((x) => x.product === item.product);

      if (existItem) {
        return {
          ...state,
          cartItems: state.cartItems.map((x) =>
            x.product === existItem.product ? item : x
          ),
        };
      } else {
        return { ...state, cartItems: [...state.cartItems, item] };
      }

    default:
      return state;
  }
};

export default cartReducers;

This is my cartReducer.js file and i get an error in this file, when switching to a case ‘CART_ADD_ITEM’

the error looks like this piece of code below

caught (in promise) TypeError: Cannot read properties of undefined (reading 'find')
at cartReducers (cartReducers.js:8:1)
at combination (redux.js:560:1)
at E (<anonymous>:1:33326)
at I (<anonymous>:1:33613)
at <anonymous>:1:37893
at Object.dispatch (redux.js:288:1)
at e (<anonymous>:1:38904)
at index.js:20:1
at dispatch (redux.js:691:1)
at cartAction.js:7:1

c