Enabled bitbucket feature and account in Spinnaker using hal but when I try to add a webhook it returns exception on bitbucket

webhook:

http://spinnaker-api.mydomain.com/webhooks/git/bitbucket

Error:

{"body":"{\"timestamp\":1540379308950,\"status\":500,\"error\":\"Internal Server Error\",\"exception\":\"java.lang.NullPointerException\",\"message\":\"Cannot get property 'username' on null object\"}","error":"Internal Server Error","exception":"com.netflix.spinnaker.kork.web.exceptions.GenericExceptionHandlers$RetrofitErrorWrapper","message":"500 ","status":500,"timestamp":1540379308951,"url":"http://spin-echo.spinnaker:8089/webhooks/git/bitbucket"}

I have enabled OAuth using google and it seems to be working fine. Do I have to do or add anything else? I am not sure what I am missing or doing wrong.

Both spinnaker and bitbucket hosted in private aws subnets.

Endpoint seems to be working when I run this on a browser:

http://spinnaker-api.mydomain.com/webhooks/git/bitbucket

I get a response:

"error": "Method Not Allowed",
"exception": "org.springframework.web.HttpRequestMethodNotSupportedException",
"message": "Request method 'GET' not supported",
"status": 405,
"timestamp": 1540381859422
}

I assume this means auth is working fine.