fix a bug of COCOdataset

utils/misc.py

@@ -56,7 +56,7 @@ def build_dataset(args, trans_config, device, is_train=False):
         dataset = COCODataset(
             img_size=args.img_size,
             data_dir=data_dir,
-            image_set='train2017',
+            image_set='train2017' if is_train else 'val2017',
             transform=train_transform,
             trans_config=trans_config,
             is_train=is_train