private SpanEvent newSpanEvent(int stackId) {
        final SpanEvent spanEvent = callStack.newInstance();
        spanEvent.markStartTime();
        spanEvent.setStackId(stackId);
        return spanEvent;
    }
Get current TraceID. If it was not set this will return null.

@return
agent-module/profiler/src/main/java/com/navercorp/pinpoint/profiler/context/DefaultTrace.java