feat: support null value for line chart

charts.go

@@ -24,6 +24,7 @@ package charts
 
 import (
 	"errors"
+	"math"
 	"sort"
 
 	"github.com/wcharczuk/go-chart/v2"
@@ -51,6 +52,18 @@ func SetDefaultHeight(height int) {
 	}
 }
 
+var nullValue = math.MaxFloat64
+
+// SetNullValue sets the null value, default is MaxFloat64
+func SetNullValue(v float64) {
+	nullValue = v
+}
+
+// GetNullValue gets the null value
+func GetNullValue() float64 {
+	return nullValue
+}
+
 type Renderer interface {
 	Render() (Box, error)
 }