feat: 라벨 인원수 음수 예외 처리

src/main/java/postman/bottler/label/domain/Label.java

@@ -2,6 +2,7 @@
 
 import lombok.Getter;
 import postman.bottler.label.dto.response.LabelResponseDTO;
+import postman.bottler.label.exception.InvalidLabelException;
 
 @Getter
 public class Label {
@@ -23,13 +24,22 @@ private Label(String imageUrl, int limitCount) {
     }
 
     public static Label createLabel(Long labelId, String imageUrl, int limitCount, int ownedCount) {
+        validateCount(limitCount);
+        validateCount(ownedCount);
         return new Label(labelId, imageUrl, limitCount, ownedCount);
     }
 
     public static Label createLabel(String imageUrl, int limitCount) {
+        validateCount(limitCount);
         return new Label(imageUrl, limitCount);
     }
 
+    private static void validateCount(int count) {
+        if (count < 0) {
+            throw new InvalidLabelException("라벨 인원수는 음수일 수 없습니다.");
+        }
+    }
+
     public LabelResponseDTO toLabelResponseDTO() {
         return new LabelResponseDTO(this.labelId, this.imageUrl);
     }