ENH: Better error message.

src/caoscrawler/identifiable_adapters.py

@@ -173,7 +173,10 @@ class IdentifiableAdapter(metaclass=ABCMeta):
         """
         if node.registered_identifiable is None:
             if raise_exception:
-                raise RuntimeError("no registered_identifiable")
+                parents = [p.name for p in node.parents]
+                parents_str = "\n".join(f"- {p}" for p in parents)
+                raise RuntimeError("No registered identifiable for node with these parents:\n"
+                                   + parents_str)
             else:
                 return False
         for prop in node.registered_identifiable.properties: