FIX: Raise correct error and make error message more understandable

src/caoscrawler/identifiable_adapters.py

@@ -236,10 +236,11 @@ startswith: bool, optional
                             refs.extend(referencing_entities[rtname])
                             found = True
             if not found:
-                raise NotImplementedError(
+                raise RuntimeError(
                     f"Could not find referencing entities of type(s): {prop.value}\n"
                     f"for registered identifiable:\n{registered_identifiable}\n"
-                    f"There were {len(referencing_entities)} referencing entities to choose from."
+                    f"There were {len(referencing_entities)} referencing entities to choose from.\n"
+                    f"This error can also occur in case of merge conflicts in the referencing entities."
                 )
         return refs