controllers/ViewPhotoAlbum.php

@@ -137,7 +137,8 @@ class ViewPhotoAlbum extends HTMLController
 				'id_tag' => $album['id_tag'],
 				'caption' => $album['tag'],
 				'link' => BASEURL . '/' . $album['slug'] . '/',
-				'thumbnail' => !empty($album['id_asset_thumb']) ? $assets[$album['id_asset_thumb']]->getImage() : null,
+				'thumbnail' => !empty($album['id_asset_thumb']) && isset($assets[$album['id_asset_thumb']])
+					? $assets[$album['id_asset_thumb']]->getImage() : null,
 			];
 		}