for compatible. (#329)

diff --git a/dubbo-samples-spi-compatible/src/main/java/org/apache/dubbo/samples/basic/spi/CompatibleServiceDiscovery.java b/dubbo-samples-spi-compatible/src/main/java/org/apache/dubbo/samples/basic/spi/CompatibleServiceDiscovery.java
index 4cfc665..64a00f2 100644
--- a/dubbo-samples-spi-compatible/src/main/java/org/apache/dubbo/samples/basic/spi/CompatibleServiceDiscovery.java
+++ b/dubbo-samples-spi-compatible/src/main/java/org/apache/dubbo/samples/basic/spi/CompatibleServiceDiscovery.java
@@ -54,6 +54,11 @@
 
     }
 
+    //For compatible, 3.0 service discovery need isDestroy to judgement.
+    public boolean isDestroy() {
+        return false;
+    }
+
     @Override
     public void unregister(ServiceInstance serviceInstance) throws RuntimeException {