[#3073]PriorityInstancePropertyDiscoveryFilter toString will invoked even when debug is not enabled (#3274)

diff --git a/handlers/handler-loadbalance/src/main/java/org/apache/servicecomb/loadbalance/filter/PriorityInstancePropertyDiscoveryFilter.java b/handlers/handler-loadbalance/src/main/java/org/apache/servicecomb/loadbalance/filter/PriorityInstancePropertyDiscoveryFilter.java
index 938f1bd..ea98ca7 100644
--- a/handlers/handler-loadbalance/src/main/java/org/apache/servicecomb/loadbalance/filter/PriorityInstancePropertyDiscoveryFilter.java
+++ b/handlers/handler-loadbalance/src/main/java/org/apache/servicecomb/loadbalance/filter/PriorityInstancePropertyDiscoveryFilter.java
@@ -93,7 +93,7 @@
         currentProperty = currentProperty.child();
       }
     }
-    LOGGER.debug("Discovery instance filter by {}", currentProperty.toString());
+    LOGGER.debug("Discovery instance filter by {}", currentProperty);
     context.putContextParameter(propertyKey, currentProperty);
 
     // stop push filter stack if property is empty