#fixed code
                                private String createSpanId() {
        try {
            return StrategySkywalkingTracerResolver.getSpanId();
        } catch (Exception e) {
            return null;
        }
    }
#vulnerable code 
                                private String createSpanId() {
        if (System.getProperties().get("skywalking.agent.service_name") == null) {
            return null;
        }

        try {
            Object traceContext = StrategySkywalkingTracerResolver.invokeStaticMethod("org.apache.skywalking.apm.agent.core.context.ContextManager", "get");
            if (traceContext != null) {
                if (traceContext.getClass().getName().equals("org.apache.skywalking.apm.agent.core.context.TracingContext")) {
                    Field fieldSegment = StrategySkywalkingTracerResolver.findField(traceContext.getClass(), "segment");
                    Object segment = StrategySkywalkingTracerResolver.getField(fieldSegment, traceContext);
                    Field fieldSegmentId = StrategySkywalkingTracerResolver.findField(segment.getClass(), "traceSegmentId");
                    String segmentId = StrategySkywalkingTracerResolver.getField(fieldSegmentId, segment).toString();

                    return segmentId;
                } else {
                    return null;
                }
            }
        } catch (Exception e) {
        }

        return null;
    } 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE