The problem is that when a post to WordPress is successful, I was trying to set the error field in your Firestore document to undefined. Firestore does not allow undefined as a field value, which is causing the updateDoc() function to fail.
To fix this, I will modify the addArticle function in src/firebase/firestore/articles.ts. When a post is successful, instead of setting the error field to undefined, I will explicitly set it to null. This is a valid value in Firestore and will correctly represent the absence of an error.
