adding validation.

bollinger_band_series.go

@@ -1,6 +1,9 @@
 package chart
 
-import "math"
+import (
+	"fmt"
+	"math"
+)
 
 // BollingerBandsSeries draws bollinger bands for an inner series.
 // Bollinger bands are defined by two lines, one at SMA+k*stddev, one at SMA-k*stdev.
@@ -147,3 +150,11 @@ func (bbs BollingerBandsSeries) getVariance(valueBuffer *RingBuffer) float64 {
 func (bbs BollingerBandsSeries) getStdDev(valueBuffer *RingBuffer) float64 {
 	return math.Pow(bbs.getVariance(valueBuffer), 0.5)
 }
+
+// Validate validates the series.
+func (bbs BollingerBandsSeries) Validate() error {
+	if bbs.InnerSeries == nil {
+		return fmt.Errorf("bollinger bands series requires InnerSeries to be set")
+	}
+	return nil
+}