clear 로 변경

src/main/java/com/eactive/eai/custom/transformer/function/userdefined/SubStringRequestMessage.java

@@ -24,10 +24,7 @@ public class SubStringRequestMessage  extends PostfixMathCommand {
         int end = toInt(p1);
 
         String resultStr = bizData.substring(start, end);
-
-        if(inStack.size() > 0){
-            inStack.pop();
-        }
+        inStack.clear();
 
         inStack.push(resultStr);
     }