Invalid descend range result about buntdb HOT 3 CLOSED

DescendRange(index, lessOrEqual, greaterThan string, iterator func(key, value string) bool) error

tx.DescendRange("last_name", `{"name":{"last":""}}`, `{"name":{"last":"Ma"}}`, func(key, value string) bool {

tx.DescendRange("last_name", `{"name":{"last":"Ma"}}`, `{"name":{"last":""}}`, func(key, value string) bool {

db, _ := buntdb.Open(":memory:")
db.Update(func(tx *buntdb.Tx) error {
	tx.CreateIndex("last_name", "*", buntdb.Desc(buntdb.IndexJSON("name.last")))

	tx.Set("1", `{"name":{"first":"Tom","last":"Johnson"},"age":"38"}`, nil)
	tx.Set("2", `{"name":{"first":"Janet","last":"Prichard"},"age":"47"}`, nil)
	tx.Set("3", `{"name":{"first":"Carol","last":"Anderson"},"age":"52"}`, nil)
	tx.Set("4", `{"name":{"first":"Alan","last":"Cooper"},"age":"28"}`, nil)
	tx.Set("5", `{"name":{"first":"Jack","last":"Ma"},"age":"20"}`, nil)
	tx.Set("6", `{"name":{"first":"Blues","last":"Li"},"age":"31"}`, nil)
	tx.Set("7", `{"name":{"first":"Pony","last":"Ma"},"age":"3"}`, nil)
	tx.Set("8", `{"name":{"first":"Robin","last":"Li"},"age":"2"}`, nil)
	tx.Set("9", `{"name":{"first":"Larry","last":"Liu"},"age":""}`, nil)
	return nil
})

db.View(func(tx *buntdb.Tx) error {
	fmt.Println("---------------------")
	tx.Ascend("last_name", func(key, value string) bool {
		fmt.Printf("%s: %s\n", key, value)
		return true
	})

	fmt.Println("---------------------")
	tx.AscendRange("last_name", `{"name":{"last":"Ma"}}`, `{"name":{"last":""}}`, func(key, value string) bool {
		fmt.Printf("%s: %s\n", key, value)
		return true
	})
	return nil
})