Urgent, please help me,I tried to use PHAssetCollection to get additional photos of the camera but returned to nil

I tried to use a mobile phone to connect my SLR cameras, connection has been a success, I can also see my SLR camera in system camera pictures, but I use fetchAssetCollectionsWithType PHAssetCollection class methods, return PHFetchResult have been nil


PHFetchResult *smartAlbums = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumImported options:nil];
  
    [smartAlbums enumerateObjectsUsingBlock:^(PHCollectionList * _Nonnull collection, NSUInteger idx, BOOL *stop) {
      
    }];