public ApolloAuditTracer tracer() {
    RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
    if (requestAttributes != null) {
      Object tracer = requestAttributes.getAttribute(ApolloAuditConstants.TRACER,
          RequestAttributes.SCOPE_REQUEST);
      if (tracer != null) {
        return ((ApolloAuditTracer) tracer);
      } else {
        ApolloAuditTracer newTracer = new ApolloAuditTracer(new ApolloAuditScopeManager(), operatorSupplier);
        setTracer(newTracer);
        return newTracer;
      }
    }
    return null;
  }
@Test
  public void testGetTracerNotInRequestThread() {
    ApolloAuditTracer get = traceContext.tracer();
    assertNull(get);
  }