Error: Argument id for data.postedBy.connect.id must not be null. Please use undefined instead.

Hi!

I'm attempting to run the two GraphQL mutations specified at the end of the this article: https://www.howtographql.com/react-apollo/1-getting-started/, but after following every step in the above, I'm getting this error that Googling has turned up blank for.

Does anyone know what's going on here?