Fix NPE in handleMethodException method of apm-jdk-threadpool-plugin. (#681)

Co-authored-by: forrestwang <forrest.wang@woo.network>

CHANGES.md

@@ -6,6 +6,7 @@ Release Notes.
 ------------------
 
 * Remove `idleCount` tag in Alibaba Druid meter plugin.
+* Fix NPE in handleMethodException method of apm-jdk-threadpool-plugin.
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/213?closed=1)
 

apm-sniffer/bootstrap-plugins/jdk-threadpool-plugin/src/main/java/org/apache/skywalking/apm/plugin/AbstractThreadingPoolInterceptor.java

@@ -63,6 +63,10 @@ public abstract class AbstractThreadingPoolInterceptor implements InstanceMethod
 
     @Override
     public void handleMethodException(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes, Throwable t) {
+        if (!ContextManager.isActive()) {
+            return;
+        }
+
         ContextManager.activeSpan().log(t);
     }
 }