Correct Null Key Suppression

internal/topdata/convert.go

@@ -453,6 +453,17 @@ func convertedRowKeyCandidates(row map[string]any, preferred []string) []string
 	fields := preferred
 	if len(fields) == 0 {
 		fields = []string{"LABEL", "Label", "Name"}
+	} else {
+		for _, field := range fields {
+			value, ok := row[field]
+			if !ok {
+				return nil
+			}
+			text := strings.TrimSpace(format2DAValue(value))
+			if text == "" || text == nullValue {
+				return nil
+			}
+		}
 	}
 	values := make([]string, 0, len(fields))
 	seen := map[string]struct{}{}