code: public TraceStep startStep(String call, IStatsProducer producer, String methodName){
  		TraceStep last = current;
  		current = new TraceStep(call, producer, methodName);
  		//it actually happened in production, we are still investigating why, but this fix should at least prevent the NPE for now.
  		if (last!=null)
  			last.addChild(current);
  		return current;
  	}
docs: Creates a new sub step in current call.