diff --git a/internal/internal.go b/internal/internal.go
new file mode 100644
index 0000000..7ea3ce4
--- /dev/null
+++ b/internal/internal.go
@@ -0,0 +1,8 @@
+package internal
+
+import "google.golang.org/grpc/balancer"
+
+var (
+	// EmptyDoneFunc is a empty done function
+	EmptyDoneFunc = func(balancer.DoneInfo) {}
+)
diff --git a/p2c/least_loaded.go b/p2c/least_loaded.go
index b6a825f..3084542 100644
--- a/p2c/least_loaded.go
+++ b/p2c/least_loaded.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/hnlq715/go-loadbalance"
+	"github.com/hnlq715/go-loadbalance/internal"
 	"google.golang.org/grpc/balancer"
 )
 
@@ -42,7 +43,7 @@ func (p *leastLoaded) Next() (interface{}, func(balancer.DoneInfo)) {
 
 	switch len(p.items) {
 	case 0:
-		return nil, func(balancer.DoneInfo) {}
+		return nil, internal.EmptyDoneFunc
 	case 1:
 		sc = p.items[0]
 	default:
diff --git a/p2c/pewma.go b/p2c/pewma.go
index 17e33b7..f050f2c 100644
--- a/p2c/pewma.go
+++ b/p2c/pewma.go
@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/hnlq715/go-loadbalance"
+	"github.com/hnlq715/go-loadbalance/internal"
 	"google.golang.org/grpc/balancer"
 )
 
@@ -88,7 +89,7 @@ func (p *pewma) Next() (interface{}, func(balancer.DoneInfo)) {
 
 	switch len(p.items) {
 	case 0:
-		return nil, func(balancer.DoneInfo) {}
+		return nil, internal.EmptyDoneFunc
 	case 1:
 		sc = p.items[0]
 	default:
diff --git a/roundrobin/smooth_weighted.go b/roundrobin/smooth_weighted.go
index f5edde9..573f41d 100644
--- a/roundrobin/smooth_weighted.go
+++ b/roundrobin/smooth_weighted.go
@@ -4,6 +4,7 @@ import (
 	"math"
 
 	"github.com/hnlq715/go-loadbalance"
+	"github.com/hnlq715/go-loadbalance/internal"
 	"google.golang.org/grpc/balancer"
 )
 
@@ -51,14 +52,14 @@ func (w *smoothRoundrobin) Reset() {
 // Next returns next selected server.
 func (w *smoothRoundrobin) Next() (interface{}, func(balancer.DoneInfo)) {
 	if w.n == 0 {
-		return nil, func(balancer.DoneInfo) {}
+		return nil, internal.EmptyDoneFunc
 	}
 
 	if w.n == 1 {
-		return w.items[0].Item, func(balancer.DoneInfo) {}
+		return w.items[0].Item, internal.EmptyDoneFunc
 	}
 
-	return nextSmoothWeighted(w.items).Item, func(balancer.DoneInfo) {}
+	return nextSmoothWeighted(w.items).Item, internal.EmptyDoneFunc
 }
 
 // nextSmoothWeighted selects the best node through the smooth weighted roundrobin .
diff --git a/roundrobin/smooth_weighted_test.go b/roundrobin/smooth_weighted_test.go
index 47824ce..26523d4 100644
--- a/roundrobin/smooth_weighted_test.go
+++ b/roundrobin/smooth_weighted_test.go
@@ -4,13 +4,15 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc/balancer"
 )
 
 func TestSW_Next(t *testing.T) {
 	w := NewSmoothRoundrobin()
 
-	s, _ := w.Next()
+	s, done := w.Next()
 	assert.Nil(t, s)
+	done(balancer.DoneInfo{})
 
 	w.Add("server1", 5)
 	s, _ = w.Next()