Contentful reference field: "fields" property null

## Description

Reference type: fields property is null.

### Steps to reproduce

1. Create a reference type in the content model:

2. For validation I entered "Accept only specified entry type: Tags".

3. I then referenced some tags in all my posts for this particular content model.

### Expected result
This was the console.log output of the node in 0.5.8:

### Actual result

In newer versions, fields is null:

### Environment

Libs:

- gridsome version: > 0.5.8