Minor updates and improvements (#216)

Co-authored-by: Hardik Dava <39372750+hardikdava@users.noreply.github.com>
Co-authored-by: Onuralp Sezer <thunderbirdtr@fedoraproject.org>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/yolo/v8/detect/val.py

@@ -43,7 +43,8 @@ class DetectionValidator(BaseValidator):
 
     def init_metrics(self, model):
         head = model.model[-1] if self.training else model.model.model[-1]
-        self.is_coco = self.data.get('val', '').endswith(f'coco{os.sep}val2017.txt')  # is COCO dataset
+        val = self.data.get('val', '')  # validation path
+        self.is_coco = isinstance(val, str) and val.endswith(f'coco{os.sep}val2017.txt')  # is COCO dataset
         self.class_map = ops.coco80_to_coco91_class() if self.is_coco else list(range(1000))
         self.args.save_json |= self.is_coco and not self.training  # run on final val if training COCO
         self.nc = head.nc