diff --git a/src/main/kotlin/com/sangdol/validation/DemoService.kt b/src/main/kotlin/com/sangdol/validation/DemoService.kt
index 32e91bf..daaa864 100644
--- a/src/main/kotlin/com/sangdol/validation/DemoService.kt
+++ b/src/main/kotlin/com/sangdol/validation/DemoService.kt
@@ -11,7 +11,7 @@ class DemoService(
 
     fun doSomething(request: SolutionForPrimitive) {
         log.info { "solution for primitive requests: $request" }
-        log.info { "value: ${request.value!!}" }
+        request.value?.let { log.info { "value: ${request.value}" } }
     }
 
     fun doSomething(request: WrapperRequest) {