Trying to use the bitbucket hook and so far as I can tell, I guess that it is sending a JSON body without specifying a user. I wasn't able to retrieve the JSON that it was sending, but it seems like that field is not a guaranteed field.

Error while serving http://104.236.89.214/bitbucket-hook/
java.lang.reflect.InvocationTargetException
...
Caused by: net.sf.json.JSONException: JSONObject["user"] not found.
at net.sf.json.JSONObject.getString(JSONObject.java:2040)
at com.cloudbees.jenkins.plugins.BitbucketHookReceiver.processPayload(BitbucketHookReceiver.java:104)
at com.cloudbees.jenkins.plugins.BitbucketHookReceiver.doIndex(BitbucketHookReceiver.java:59)

The offending line:
String user = payload.getString("user");