diff --git a/src/tracksdata/graph/_test/test_graph_backends.py b/src/tracksdata/graph/_test/test_graph_backends.py
index fc52fe59..86c9693f 100644
--- a/src/tracksdata/graph/_test/test_graph_backends.py
+++ b/src/tracksdata/graph/_test/test_graph_backends.py
@@ -2288,7 +2288,7 @@ def _fill_mock_geff_graph(graph_backend: BaseGraph) -> None:
     )
     graph_backend.add_node_attr_key(DEFAULT_ATTR_KEYS.MASK, pl.Object)
     graph_backend.add_node_attr_key(DEFAULT_ATTR_KEYS.TRACKLET_ID, pl.Int64)
-    graph_backend.add_node_attr_key("ndfeature", pl.Object)
+    graph_backend.add_node_attr_key("ndfeature", pl.Array(pl.Float64, (3, 1)), np.ones((3, 1)))
 
     graph_backend.add_edge_attr_key("weight", pl.Float64)
 
diff --git a/src/tracksdata/metrics/_ctc_metrics.py b/src/tracksdata/metrics/_ctc_metrics.py
index 39640508..876cb54a 100644
--- a/src/tracksdata/metrics/_ctc_metrics.py
+++ b/src/tracksdata/metrics/_ctc_metrics.py
@@ -104,7 +104,8 @@ def _match_single_frame(
         # loading original group ids and filtering by the matches
         _mapped_ref = ref_group[reference_graph_key][rows_id].to_list()
         _mapped_comp = comp_group[input_graph_key][cols_id].to_list()
-        _ious = weights[rows_id, cols_id].tolist()
+        _ious = weights[rows_id, cols_id]
+        _ious = _ious.tolist() if _ious.size > 0 else []
 
         LOG.info("Done!")