fix异常被吞没的问题

Author: lvyahui8

spring-boot-data-aggregator-example/src/main/java/io/github/lvyahui8/spring/example/interceptor/SampleAggregateQueryInterceptor.java

@@ -28,7 +28,8 @@ public void queryBefore(AggregationContext aggregationContext, DataProvideDefini
 
     @Override
     public Object queryAfter(AggregationContext aggregationContext, DataProvideDefinition provideDefinition, Object result) {
-        log.info("query after. provider:{},result:{}",provideDefinition.getMethod().getName(),result.toString());
+        log.info("query after. provider:{},result:{}",provideDefinition.getMethod().getName(),result != null ?
+                result.toString() : "null");
         return result;
     }