Fix issue #5795 (#5797)

* Fix issue #5795 

Fix the issue: nutz plugin throw NPE at afterMethod, cause traceid keep unchange for the thread

* fix the style and modify the CHANGES.md
Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>
Co-authored-by: Nsimonlei <simonlei@tencent.com>
Co-authored-by: Nkezhenxu94 <kezhenxu94@apache.org>

CHANGES.md

@@ -15,6 +15,7 @@ Release Notes.
 * Make the okhttp3 plugin to support Java 14
 * Polish tracing context related codes.
 * Add the plugin for async-http-client 2.x
+* Fix NPE in the nutz plugin.
 
 #### OAP-Backend
 * Add the `@SuperDataset` annotation for BrowserErrorLog.

apm-sniffer/apm-sdk-plugin/nutz-plugins/http-1.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/nutz/http/sync/SenderSendInterceptor.java

@@ -63,11 +63,12 @@ public class SenderSendInterceptor implements InstanceMethodsAroundInterceptor {
     public Object afterMethod(final EnhancedInstance objInst, final Method method, final Object[] allArguments,
         final Class<?>[] argumentsTypes, Object ret) throws Throwable {
         Response response = (Response) ret;
-        int statusCode = response.getStatus();
         AbstractSpan span = ContextManager.activeSpan();
-        if (statusCode >= 400) {
+
+        if (response == null || response.getStatus() >= 400) {
             span.errorOccurred();
-            Tags.STATUS_CODE.set(span, Integer.toString(statusCode));
+            if (response != null)
+                Tags.STATUS_CODE.set(span, Integer.toString(response.getStatus()));
         }
         ContextManager.stopSpan();
         return ret;