swagger validator complains about _links as an extra property

[travi]

{
    "messages": ["attribute _links is unexpected"],
    "schemaValidationMessages": [{
        "level": "error",
        "domain":"validation",
        "keyword":"additionalProperties", 
        "message": "object instance has properties which are not allowed by the schema: [\"_links\"]",
        "schema": {
            "loadingURI": "#",
            "pointer": ""
        },
        "instance": {"pointer":""}
    }]
}