Bad TODO List Example

The error is in this link:
const serverURL = '[https://uofye.sse.codesandbox.io/](https://uofye.sse.codesandbox.io/)';

The TodoList example in [docs](https://www.apollographql.com/docs/react/performance/optimistic-ui#:~:text=object%20is%20cached.-,View%20on%20CodeSandbox,-You%20can%20view) is a bad example as it returns an error:

When you try to create an item, it throws the following:

The sandbox environment also doesn't work and cloning the docs-examples repo and locally running the server and client also results in the same error.

Start with the TodoList example linked from the Apollo optimistic UI documentation and reproduce the error when creating an item in its CodeSandbox. Compare that result with the locally cloned docs-examples repository; done means the example runs successfully and creating an item no longer throws the reported error.

Written by the indexing model from the issue text.