Implement transformNull

pkg/datasource/functions.go

@@ -60,6 +60,7 @@ func init() {
 		"groupBy":       applyGroupBy,
 		"scale":         applyScale,
 		"offset":        applyOffset,
+		"transformNull": applyTransformNull,
 		"percentile":    applyPercentile,
 		"timeShift":     applyTimeShiftPost,
 	}
@@ -202,6 +203,16 @@ func applyOffset(series timeseries.TimeSeries, params ...interface{}) (timeserie
 	return series.Transform(transformFunc), nil
 }
 
+func applyTransformNull(series timeseries.TimeSeries, params ...interface{}) (timeseries.TimeSeries, error) {
+	nullValue, err := MustFloat64(params[0])
+	if err != nil {
+		return nil, errParsingFunctionParam(err)
+	}
+
+	transformFunc := timeseries.TransformNull(nullValue)
+	return series.Transform(transformFunc), nil
+}
+
 func applyAggregateBy(series []*timeseries.TimeSeriesData, params ...interface{}) ([]*timeseries.TimeSeriesData, error) {
 	pInterval, err := MustString(params[0])
 	pAgg, err := MustString(params[1])

pkg/timeseries/transform_functions.go

@@ -14,6 +14,12 @@ func TransformOffset(offset float64) TransformFunc {
 	}
 }
 
+func TransformNull(nullValue float64) TransformFunc {
+	return func(point TimePoint) TimePoint {
+		return transformNull(point, nullValue)
+	}
+}
+
 func TransformShiftTime(interval time.Duration) TransformFunc {
 	return func(point TimePoint) TimePoint {
 		return transformShiftTime(point, interval)
@@ -41,3 +47,10 @@ func transformShiftTime(point TimePoint, interval time.Duration) TimePoint {
 	point.Time = shiftedTime
 	return point
 }
+
+func transformNull(point TimePoint, nullValue float64) TimePoint {
+	if point.Value == nil {
+		point.Value = &nullValue
+	}
+	return point
+}