title: cannot increment item in cart
body: <p>i wanna increment the item quantity whenever i add an item to cart. My codes aren't working and i get the error &quot;<em>Cannot read properties of undefined (reading 'length')</em>&quot; at my Cart.js and i don't know why. Can anyone help me? Thank you so much!</p>
  <p>Codesandbox link:<a href="https://codesandbox.io/s/redux-shop-cart-forked-tlpek?file=/src/components/Cart.js" rel="nofollow noreferrer">https://codesandbox.io/s/redux-shop-cart-forked-tlpek?file=/src/components/Cart.js</a></p>