fix: if mappings are empty

Author: djs0109

semantic_iot/RML_preprocess.py

@@ -410,6 +410,8 @@ def suggestion_condition_top_matches(self, n: int, mappings: List[tuple]) -> dic
         n: number of top matches to consider
         mappings: list of tuples (iri, score)
         """
+        if not mappings:
+            return {}
         # sort the mappings by score
         mappings.sort(key=lambda x: x[1], reverse=True)