From 70e51bb352b9ac0276fb5739a80825d1f2714c59 Mon Sep 17 00:00:00 2001
From: aimuz <mr.imuz@gmail.com>
Date: Thu, 24 Mar 2022 21:41:38 +0800
Subject: [PATCH] fix: empty slice are set to nil (#1702)

support for empty slce, Same behavior as json.Unmarshal
---
 core/mapping/unmarshaler.go      |  6 ++++++
 core/mapping/unmarshaler_test.go | 14 ++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/core/mapping/unmarshaler.go b/core/mapping/unmarshaler.go
index 38703744..780b2420 100644
--- a/core/mapping/unmarshaler.go
+++ b/core/mapping/unmarshaler.go
@@ -450,6 +450,12 @@ func (u *Unmarshaler) fillSlice(fieldType reflect.Type, value reflect.Value, map
 	refValue := reflect.ValueOf(mapValue)
 	conv := reflect.MakeSlice(reflect.SliceOf(baseType), refValue.Len(), refValue.Cap())
 
+	// support for empty slice
+	if !refValue.IsNil() && refValue.Len() == 0 {
+		value.Set(conv)
+		return nil
+	}
+
 	var valid bool
 	for i := 0; i < refValue.Len(); i++ {
 		ithValue := refValue.Index(i).Interface()
diff --git a/core/mapping/unmarshaler_test.go b/core/mapping/unmarshaler_test.go
index 767dc0d7..e71adca2 100644
--- a/core/mapping/unmarshaler_test.go
+++ b/core/mapping/unmarshaler_test.go
@@ -330,28 +330,34 @@ func TestUnmarshalFloat(t *testing.T) {
 
 func TestUnmarshalInt64Slice(t *testing.T) {
 	var v struct {
-		Ages []int64 `key:"ages"`
+		Ages  []int64 `key:"ages"`
+		Slice []int64 `key:"slice"`
 	}
 	m := map[string]interface{}{
-		"ages": []int64{1, 2},
+		"ages":  []int64{1, 2},
+		"slice": []interface{}{},
 	}
 
 	ast := assert.New(t)
 	ast.Nil(UnmarshalKey(m, &v))
 	ast.ElementsMatch([]int64{1, 2}, v.Ages)
+	ast.Equal([]int64{}, v.Slice)
 }
 
 func TestUnmarshalIntSlice(t *testing.T) {
 	var v struct {
-		Ages []int `key:"ages"`
+		Ages  []int `key:"ages"`
+		Slice []int `key:"slice"`
 	}
 	m := map[string]interface{}{
-		"ages": []int{1, 2},
+		"ages":  []int{1, 2},
+		"slice": []interface{}{},
 	}
 
 	ast := assert.New(t)
 	ast.Nil(UnmarshalKey(m, &v))
 	ast.ElementsMatch([]int{1, 2}, v.Ages)
+	ast.Equal([]int{}, v.Slice)
 }
 
 func TestUnmarshalString(t *testing.T) {