BENCH-155 code readability improved

Author: AudriusPutys

src/main/java/com/answerdigital/answerking/exception/util/RestResponseEntityExceptionHandler.java

@@ -35,9 +35,9 @@ public ResponseEntity<ErrorResponse> handleMethodArgumentNotValidException(
                         .stream()
                         .collect(Collectors.toMap(FieldError::getField,
                                 FieldError -> new ArrayList<>(Collections.singletonList(FieldError.getDefaultMessage())),
-                                (l1, l2) -> {
-                                    l1.addAll(l2);
-                                    return l1;
+                                (mainList, newList) -> {
+                                    mainList.addAll(newList);
+                                    return mainList;
                                 }));
 
         final ErrorResponse response = new ValidationErrorResponse(new ValidationException(errorsMap), request);