Sending sparse fields sets for a non-existent resource type does not give clear error message

[lindyhopchris]

By accident I sent sparse fields for the post resource, instead of posts. This resulted in the following error:

{
    "errors": [
        {
            "detail": "Sparse field sets post.slug, post.synopsis, post.title are not allowed.",
            "source": {
                "parameter": "fields"
            },
            "status": "400",
            "title": "Invalid Query Parameter"
        }
    ],
    "jsonapi": {
        "version": "1.0"
    }
}

The message should probably actually say that the post resource type does not exist.