Small issue with Create conversation endpoint

When call API to create a conversation with empty `body` and one file attached, the API response with an error, but on https://app.intercom.com/a/inbox/ the chat appear.

Here an example of CURL:

```bash

curl --location 'https://api.intercom.io/conversations' \
--header 'Authorization: Bearer <admin_token>' \
--header 'Content-Type: application/json' \
--header 'Intercom-Version: 2.10' \
--data '{
    "from": {
        "type": "user",
        "id": "<contact_id>"
    },
    "subject": "Test Subject",
    "attachment_urls": [
        "https://picsum.photos/seed/picsum/512/512"
    ]
}'

```

The example of response:

```JSON

{
    "type": "error.list",
    "request_id": "0035jabkv5b82qmiu3cg",
    "errors": [
        {
            "code": "server_error",
            "message": "Server Error"
        }
    ]
}

```