TextItemNormalizer issue with body field on node

We encountered an issue with the TextItemNormalizer when using the default_content module to export content in HAL JSON format. This was with a new node content type - no additional fields or anything like that.

The issue was discovered when trying to export content and then re-import using the default_content module when replication is also enabled.

(I did a test with the OOTB 'Article' content type and just visually checked the serializer output - on inspection, it seems to be an issue there too).

Steps:

1. Create a new node content type, and just accept the defaults.
2. Create some new content, make a note of the nid.
3. Serialize the entity. I've been using the following test code using `drush scr` in a terminal.

$entity = \Drupal\node\Entity\Node::load(3);
$serializer = \Drupal::service('serializer');

print_r($serializer->serialize($entity, 'hal_json', ['json_encode_options' => JSON_PRETTY_PRINT]));

Essentially, when replication is disabled, the body field is serialized as follows :-

...
    "body": [
        {
            "value": "<p>It's a test!<\/p>\r\n",
            "format": "basic_html",
            "summary": "",
            "lang": "en"
        }
    ]
}

However, when replication is enabled, we get a missing 'body' key :

...
    ],
    "value": "<p>It's a test!<\/p>\r\n",
    "format": "basic_html",
    "processed": "<p>It's a test!<\/p>",
    "summary": "",
    "summary_processed": ""
}