refactor: lateinit 필드 지정으로 인한 불필요한 !! 연산자 제거

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) {

src/test/kotlin/com/sangdol/validation/DemoControllerTest.kt

@@ -21,7 +21,7 @@ import org.springframework.test.web.servlet.result.MockMvcResultMatchers.status
 class DemoControllerTest {
 
     @Autowired
-    private val mockMvc: MockMvc? = null
+    private lateinit var mockMvc: MockMvc
 
     @DisplayName("Wrapper 타입인 경우 값이 입력되지 않으면 HttpMessageNotReadableException이 발생한다.")
     @ParameterizedTest(name = "{0}")
@@ -76,7 +76,7 @@ class DemoControllerTest {
         }
     }
 
-    private fun run(endpoint: String, body: String, expectedStatus: Int): ResultActions = mockMvc!!
+    private fun run(endpoint: String, body: String, expectedStatus: Int): ResultActions = mockMvc
         .perform(
             post(endpoint)
                 .contentType(MediaType.APPLICATION_JSON_VALUE)