Merge remote-tracking branch 'upstream/master'

src/main/java/com/alibaba/druid/pool/DruidDataSource.java

@@ -2745,7 +2745,9 @@ public class DruidDataSource extends DruidAbstractDataSource
 
     @Override
     public ObjectName preRegister(MBeanServer server, ObjectName name) throws Exception {
-        return null;
+        //do nothing
+        //return original name to avoid NullPointerException
+        return name;
     }
 
     @Override