rdflibloader: fix various None issues

Author: joshmoore

linkml_runtime/loaders/rdflib_loader.py

@@ -130,6 +130,8 @@ def from_rdf_graph(self, graph: Graph, schemaview: SchemaView, target_class: Typ
                             # back to a text representation
                             v = namespaces.curie_for(o)
                             e = schemaview.get_enum(slot.range)
+                            if e is None:
+                                raise ValueError(f'no enum found for {slot.range}: {o} (ns={v})')
                             for pv in e.permissible_values.values():
                                 if v == pv.meaning or str(o) == pv.meaning:
                                     v = pv.text
@@ -169,9 +171,16 @@ def from_rdf_graph(self, graph: Graph, schemaview: SchemaView, target_class: Typ
         # Step 2: replace inline pointers with object dicts
         def repl(v):
             if isinstance(v, Pointer):
-                v2 = obj_map[v.obj]
+                v2 = obj_map.get(v.obj)
                 if v2 is None:
-                    raise Exception(f'No mapping for pointer {v}')
+                    msg = f'No mapping for pointer {v}. Triples:'
+                    for s, p, o in graph.triples((None, None, v.obj)):
+                        for s2, p2, o2 in graph.triples((None, None, s)):
+                            msg += f"\n{s2} {p2} {o2}."
+                        msg += f"\n{s} {p} {o}."
+                    for s, p, o in graph.triples((v.obj, None, None)):
+                        msg += f"\n{s} {p} {o}."
+                    raise Exception(msg)
                 return v2
             else:
                 return v