Event > create "found unpermitted parameters: metadata" error

[ebuildy]

In Php, empty associative array are JSON encoded as "[]" and so, sending:

POST https://api.intercom.io/events
{"created_at":1430841996,"event_name":"merchant_created","metadata":[],"user_id":"1"}

Gives

{
    "type": "error.list",
    "request_id": "7e654619-03e4-43e8-aaef-8d0c82850bf2",
    "errors": [
        {
            "code": "parameter_invalid",
            "message": "found unpermitted parameters: metadata"
        }
    ]
}

A possible solution would be to remove metadata field is it's empty.