diff --git a/src/main/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverter.java b/src/main/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverter.java
index ede6d74..0103489 100644
--- a/src/main/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverter.java
+++ b/src/main/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverter.java
@@ -62,7 +62,7 @@ public final class QuizDtoConverter {
 
     private static String getAnswerResourceId(final Quiz quiz) {
         return (quiz.getAnswer() == null)
-                ? StringUtils.EMPTY
+                ? null
                 : quiz.getAnswer().getResourceId();
     }
 
diff --git a/src/test/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverterTest.java b/src/test/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverterTest.java
index 6ca6926..66d17b2 100644
--- a/src/test/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverterTest.java
+++ b/src/test/java/com/mangkyu/employment/interview/app/quiz/converter/QuizDtoConverterTest.java
@@ -84,7 +84,7 @@ class QuizDtoConverterTest {
         assertThat(result.getQuizLevelList().size()).isEqualTo(quiz.getQuizLevel().size());
         assertThat(result.getCreatedAt()).isEqualTo(Timestamp.valueOf(quiz.getCreatedAt()).getTime());
         assertThat(result.getCategory().getCode()).isEqualTo(enumMapperValue(quiz.getQuizCategory()).getCode());
-        assertThat(result.getAnswerResourceId()).isEqualTo(StringUtils.EMPTY);
+        assertThat(result.getAnswerResourceId()).isNull();
     }
 
     @Test
@@ -120,7 +120,7 @@ class QuizDtoConverterTest {
         assertThat(result.getQuizLevelList().size()).isEqualTo(quiz.getQuizLevel().size());
         assertThat(result.getCreatedAt()).isEqualTo(Timestamp.valueOf(quiz.getCreatedAt()).getTime());
         assertThat(result.getCategory()).isNull();
-        assertThat(result.getAnswerResourceId()).isEqualTo(StringUtils.EMPTY);
+        assertThat(result.getAnswerResourceId()).isNull();
     }
 
     private EnumMapperValue enumMapperValue(final EnumMapperType enumMapperType) {