Calling logout without session throws error

[brsanthu]

/logout actions should be idempotent so calling repeatedly even without any session in place, should return successfully.

But as of now, calling /logout without a valid session, throws following error

{
    "message": "Required argument [Authentication authentication] not specified",
    "path": "/authentication",
    "_links": {
        "self": {
            "href": "/logout",
            "templated": false
        }
    }
}