fix empty metrics

app.py

@@ -113,7 +113,10 @@ def retrieve_dataframes(
                         # assuming that WER is given in 0.13 format
                         result = 100 * result
                     elif isinstance(result, list):
-                        result = result[0]
+                        if len(result) > 0:
+                            result = result[0]
+                        else:
+                            result = None
                         
                     results[model_id] = round(result, 2) if result is not None else None