Add more

data/time_series.go

@@ -420,7 +420,7 @@ func WideToLong(wideFrame *Frame) (*Frame, error) {
 	if err != nil {
 		return nil, err
 	} else if wideLen == 0 {
-		return nil, fmt.Errorf("can not convert to long series, input fields have no rows")
+		return nil, ErrInputFieldsWithoutRows
 	}
 
 	var uniqueValueNames []string                        // unique names of Fields that are value types

data/time_series_errors.go

@@ -5,6 +5,7 @@ import "errors"
 var (
 	ErrorNullTimeValues = errors.New("unable to process the data to wide series because input has null time values, make sure all time values are not null")
 	ErrorSeriesUnsorted = errors.New("unable to process the data because it is not sorted in ascending order by time, please updated your query to sort the data by time and try again")
+	ErrInputFieldsWithoutRows = errors.New("can not convert to long series, input fields have no rows")
 )