Fixes Cart page sign out error when cart does not exist in cache

[supernova-at]

Description

This PR provides a fallback empty object ({}) to avoid a destructuring exception thrown when the cart does not exist in our Apollo cache.

This surfaced on the /cart page after the user signed out: the cache was cleared out using Apollo client's resetStore. But resetStore also causes all active queries to be refetched. GiftOptions has one such query that was querying for the cart in the cache. Because it was just cleared out via resetStore, the query got back undefined, which the code then attempted to destructure.

Providing the fallback empty object in the case of undefined returns the expected result (undefined values for include_gift_receipt, include_printed_card, and gift_message), and results in the ability to sign out from the cart page without error.

Related Issue

Closes PWA-368.

Acceptance

Verification Stakeholders

@revanth0212

Specification

Verification Steps

1. Sign in
2. Ensure an item is added to your cart
3. Navigate to the /cart page
4. Verify that you can sign out successfully without error
5. Sign in
6. Verify that your cart is restored to its previous state

Screenshots / Screen Captures (if appropriate)

Checklist

• I have updated the documentation accordingly, if necessary.
• I have added tests to cover my changes, if necessary.

[PWAStudioBot]

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📖	Access a deployed version of this PR here. Make sure to wait for the "pwa-pull-request-deploy" job to complete.
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📖	Associated JIRA tickets: PWA-368.

Generated by 🚫 dangerJS against e512d61

[sirugh]

I wonder what GraphQL suggests for client side caching/resolvers for this situation. We will likely run into it elsewhere - I wonder if there is some sort of "reset callback" that can reset the store to an initial state. After all, we call resetStore on sign out which was effectively deleting the cache, causing this to throw. Maybe resetStore takes a callback?

This is fine, by the way - just postulating.

[sirugh]

Oh hey: https://www.apollographql.com/docs/react/caching/cache-interaction/#resetting-the-store

[revanth0212]

Yes, I tried that a while ago when I was developing gift options. The problem is our gift options are name spaced to a certain cart id. Reset store, at that time, would not know which cart id to use to reset the store with empty gift options.

[sirugh]

Oh yeah @revanth0212 I forgot about that. So instead of doing it on store reset we would have to know to set that initial state whenever a cart is created. Hmm interesting! I don't think we can do that with the way that carts are created right now.