Update error messages from invalid sub_graph in model instantiation

CHANGELOG.md

@@ -16,6 +16,8 @@ Keep it human-readable, your future self will thank you!
 
 ### Changed
 
+- New error messages for wrongs graphs.
+
 ### Removed
 
 ## 0.2.0

src/anemoi/models/layers/mapper.py

@@ -134,8 +134,8 @@ def _register_edges(
         trainable_size : int
             Trainable tensor size
         """
-        if edge_attributes is None:
-            raise ValueError("Edge attributes must be provided")
+        assert sub_graph, f"{self.__class__.__name__} needs a valid sub_graph to register edges."
+        assert edge_attributes is not None, "Edge attributes must be provided"
 
         edge_attr_tensor = torch.cat([sub_graph[attr] for attr in edge_attributes], axis=1)