How to recursively find the userId that triggered the build in Jenkins

find_trigger_user_id.groovy

import net.sf.json.JSONException
node {
   // Just example of how to use the function
   currentBuild.description =  find_trigger_user(currentBuild)
}

def find_trigger_user(build){
    cause = build.buildCauses.getJSONObject(0)
    try{
        return cause.getString("userId")
    }catch (JSONException e){
        println("Not directly triggerred. Checking upstream")
    }
    possibleUser = null
    build.upstreamBuilds.each{
        println(build.buildCauses.toString())
        possibleUser = find_trigger_user(it)
        if (possibleUser != null)
            return
    }
    return possibleUser
}