fail if isSet not resolved

ledger/file.go

@@ -128,5 +128,10 @@ func (files Files) Deltas(like ...Like) (Deltas, error) {
 			}
 		}
 	}
+	for i := range result {
+		if result[i].isSet {
+			return nil, fmt.Errorf("failed to resolve isSet: %+v", result[i])
+		}
+	}
 	return result.Like(like...), nil
 }