执行器回调线程优化，回调地址为空时销毁问题修复；

doc/XXL-JOB官方文档.md

-## 《分布式任务调度平台XXL-JOB》
+## 《分布式任务调度平台XXL-JOB》
@@ -1478,6 +1478,7 @@ Tips: 历史版本(V1.3.x)目前已经Release至稳定版本, 进入维护阶段
 - 12、首页调度报表的日期排序在TIDB下乱序问题修复；
 - 13、调度中心与执行器双向通讯超时时间调整为3s；
 - 14、调度组件销毁流程优化，先停止调度线程，然后等待时间轮内存量任务处理完成，最终销毁时间轮线程；
+- 15、执行器回调线程优化，回调地址为空时销毁问题修复；
 
 
 ### 6.26 版本 v2.1.1 Release Notes[规划中]

xxl-job-core/pom.xml

@@ -44,31 +44,11 @@
 			<scope>provided</scope>
 		</dependency>
 
+		<!-- junit -->
 		<dependency>
-			<groupId>org.powermock</groupId>
-			<artifactId>powermock-api-mockito</artifactId>
-			<version>1.6.5</version>
-			<scope>test</scope>
-		</dependency>
-
-		<dependency>
-			<groupId>org.powermock</groupId>
-			<artifactId>powermock-module-junit4</artifactId>
-			<version>1.6.5</version>
-			<scope>test</scope>
-		</dependency>
-
-		<dependency>
-			<groupId>org.mockito</groupId>
-			<artifactId>mockito-all</artifactId>
-			<version>1.10.19</version>
-			<scope>test</scope>
-		</dependency>
-
-		<dependency>
-			<groupId>com.diffblue</groupId>
-			<artifactId>deeptestutils</artifactId>
-			<version>1.9.0</version>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>${junit.version}</version>
 			<scope>test</scope>
 		</dependency>
 

xxl-job-core/src/main/java/com/xxl/job/core/thread/TriggerCallbackThread.java

@@ -133,20 +133,25 @@ public class TriggerCallbackThread {
     public void toStop(){
         toStop = true;
         // stop callback, interrupt and wait
-        triggerCallbackThread.interrupt();
-        try {
-            triggerCallbackThread.join();
-        } catch (InterruptedException e) {
-            logger.error(e.getMessage(), e);
+        if (triggerCallbackThread != null) {    // support empty admin address
+            triggerCallbackThread.interrupt();
+            try {
+                triggerCallbackThread.join();
+            } catch (InterruptedException e) {
+                logger.error(e.getMessage(), e);
+            }
         }
 
         // stop retry, interrupt and wait
-        triggerRetryCallbackThread.interrupt();
-        try {
-            triggerRetryCallbackThread.join();
-        } catch (InterruptedException e) {
-            logger.error(e.getMessage(), e);
+        if (triggerRetryCallbackThread != null) {
+            triggerRetryCallbackThread.interrupt();
+            try {
+                triggerRetryCallbackThread.join();
+            } catch (InterruptedException e) {
+                logger.error(e.getMessage(), e);
+            }
         }
+
     }
 
     /**