diff --git a/skywalking-protocol/src/main/java/com/ai/cloud/skywalking/protocol/Span.java b/skywalking-protocol/src/main/java/com/ai/cloud/skywalking/protocol/Span.java
index d689395ff..1a7d4d01b 100644
--- a/skywalking-protocol/src/main/java/com/ai/cloud/skywalking/protocol/Span.java
+++ b/skywalking-protocol/src/main/java/com/ai/cloud/skywalking/protocol/Span.java
@@ -210,7 +210,7 @@ public class Span {
 
     public void setInvokeResult(String result){
         if (result == null){
-            result = "";
+            result = "null";
         }
         this.parameters.put(INVOKE_RESULT_PARAMETER_KEY, result);
     }