fix: resolve top 5 SonarQube issues (weekly sweep)

src/main/java/io/spring/api/ArticleApi.java

@@ -33,7 +33,7 @@ public class ArticleApi {
   private ArticleCommandService articleCommandService;
 
   @GetMapping
-  public ResponseEntity<?> article(
+  public ResponseEntity<Map<String, Object>> article(
       @PathVariable("slug") String slug, @AuthenticationPrincipal User user) {
     return articleQueryService
         .findBySlug(slug, user)
@@ -42,7 +42,7 @@ public ResponseEntity<?> article(
   }
 
   @PutMapping
-  public ResponseEntity<?> updateArticle(
+  public ResponseEntity<Map<String, Object>> updateArticle(
       @PathVariable("slug") String slug,
       @AuthenticationPrincipal User user,
       @Valid @RequestBody UpdateArticleParam updateArticleParam) {

src/main/java/io/spring/api/CommentsApi.java

@@ -38,7 +38,7 @@ public class CommentsApi {
   private CommentQueryService commentQueryService;
 
   @PostMapping
-  public ResponseEntity<?> createComment(
+  public ResponseEntity<Map<String, Object>> createComment(
       @PathVariable("slug") String slug,
       @AuthenticationPrincipal User user,
       @Valid @RequestBody NewCommentParam newCommentParam) {

src/main/java/io/spring/api/exception/InvalidRequestException.java

@@ -4,7 +4,7 @@
 
 @SuppressWarnings("serial")
 public class InvalidRequestException extends RuntimeException {
-  private final Errors errors;
+  private final transient Errors errors;
 
   public InvalidRequestException(Errors errors) {
     super("");

src/main/java/io/spring/infrastructure/mybatis/DateTimeHandler.java

@@ -15,30 +15,32 @@
 @MappedTypes(DateTime.class)
 public class DateTimeHandler implements TypeHandler<DateTime> {
 
-  private static final Calendar UTC_CALENDAR = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
+  private static final TimeZone UTC_TIMEZONE = TimeZone.getTimeZone("UTC");
 
   @Override
   public void setParameter(PreparedStatement ps, int i, DateTime parameter, JdbcType jdbcType)
       throws SQLException {
     ps.setTimestamp(
-        i, parameter != null ? new Timestamp(parameter.getMillis()) : null, UTC_CALENDAR);
+        i,
+        parameter != null ? new Timestamp(parameter.getMillis()) : null,
+        Calendar.getInstance(UTC_TIMEZONE));
   }
 
   @Override
   public DateTime getResult(ResultSet rs, String columnName) throws SQLException {
-    Timestamp timestamp = rs.getTimestamp(columnName, UTC_CALENDAR);
+    Timestamp timestamp = rs.getTimestamp(columnName, Calendar.getInstance(UTC_TIMEZONE));
     return timestamp != null ? new DateTime(timestamp.getTime()) : null;
   }
 
   @Override
   public DateTime getResult(ResultSet rs, int columnIndex) throws SQLException {
-    Timestamp timestamp = rs.getTimestamp(columnIndex, UTC_CALENDAR);
+    Timestamp timestamp = rs.getTimestamp(columnIndex, Calendar.getInstance(UTC_TIMEZONE));
     return timestamp != null ? new DateTime(timestamp.getTime()) : null;
   }
 
   @Override
   public DateTime getResult(CallableStatement cs, int columnIndex) throws SQLException {
-    Timestamp ts = cs.getTimestamp(columnIndex, UTC_CALENDAR);
+    Timestamp ts = cs.getTimestamp(columnIndex, Calendar.getInstance(UTC_TIMEZONE));
     return ts != null ? new DateTime(ts.getTime()) : null;
   }
 }

src/test/java/io/spring/infrastructure/service/DefaultJwtServiceTest.java

@@ -13,7 +13,8 @@ public class DefaultJwtServiceTest {
 
   @BeforeEach
   public void setUp() {
-    jwtService = new DefaultJwtService("123123123123123123123123123123123123123123123123123123123123", 3600);
+    jwtService =
+        new DefaultJwtService("123123123123123123123123123123123123123123123123123123123123", 3600);
   }
 
   @Test