Pre Merge pull request !20 from 陈志艺/N/A

xxl-job-core/src/main/java/com/xxl/job/core/executor/XxlJobExecutor.java

@@ -155,7 +155,9 @@ public class XxlJobExecutor  {
     private void stopEmbedServer() {
         // stop provider factory
         try {
+            if (null != embedServer) { 
                embedServer.stop();                                                                                                                                                                                                                                       
+            }
         } catch (Exception e) {
             logger.error(e.getMessage(), e);
         }