adding validation.

ema_series.go

@@ -1,5 +1,7 @@
 package chart
 
+import "fmt"
+
 const (
 	// DefaultEMAPeriod is the default EMA period used in the sigma calculation.
 	DefaultEMAPeriod = 12
@@ -99,3 +101,11 @@ func (ema *EMASeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, de
 	style := ema.Style.InheritFrom(defaults)
 	Draw.LineSeries(r, canvasBox, xrange, yrange, style, ema)
 }
+
+// Validate validates the series.
+func (ema *EMASeries) Validate() error {
+	if ema.InnerSeries == nil {
+		return fmt.Errorf("ema series requires InnerSeries to be set")
+	}
+	return nil
+}