Webhooks not working from GitLab

Hello,
I have the same error for slack integration, works fine with curl, but fails from slack with following log:

[2015/10/30 08:27:29 UTC] [EROR] /hooks/4nxy6qkf97n8ur8p6yypzuezhh:incomingWebhook code=500 rid=ocsxcf7j8iys9m7m577ajk7xbo uid= ip=54.165.66.184 No text specified [details: ]

Here's the POST request:

POST /hooks/4nxy6qkf97n8ur8p6yypzuezhh HTTP/1.1
User-Agent: Slackbot 1.0 (+https://api.slack.com/robots)
Host: mm.test.com
Accept: */*
Accept-Encoding: gzip,deflate
Content-Length: 238
Content-Type: application/x-www-form-urlencoded
Cache-Control: max-age=259200
Connection: keep-alive

token=justatoken&team_id=ourteamid&team_domain=ourdomain&service_id=13549101282&channel_id=C04ESECHD&channel_name=dev-custom-support&timestamp=1446193643.000082&user_id=U031QGRTP&user_name=jirka&text=pour+la+capture+wireshark

Many thanks,
Jirka