add test for unaddressable value in preload

preload_test.go

@@ -772,6 +772,67 @@ func TestManyToManyPreloadForPointer(t *testing.T) {
 	}
 }
 
+func TestNilPointerSlice(t *testing.T) {
+	type (
+		Level3 struct {
+			ID    uint `gorm:"primary_key;"`
+			Value string
+		}
+		Level2 struct {
+			ID       uint `gorm:"primary_key;"`
+			Value    string
+			Level3ID uint
+			Level3   *Level3
+		}
+		Level1 struct {
+			ID       uint `gorm:"primary_key;"`
+			Value    string
+			Level2ID uint
+			Level2   *Level2
+		}
+	)
+
+	DB.DropTableIfExists(&Level3{})
+	DB.DropTableIfExists(&Level2{})
+	DB.DropTableIfExists(&Level1{})
+
+	if err := DB.AutoMigrate(&Level3{}, &Level2{}, &Level1{}).Error; err != nil {
+		panic(err)
+	}
+
+	want := Level1{Value: "Bob", Level2: &Level2{
+		Value: "en",
+		Level3: &Level3{
+			Value: "native",
+		},
+	}}
+	if err := DB.Save(&want).Error; err != nil {
+		panic(err)
+	}
+
+	want2 := Level1{Value: "Tom", Level2: nil}
+	if err := DB.Save(&want2).Error; err != nil {
+		panic(err)
+	}
+
+	var got []Level1
+	if err := DB.Debug().Preload("Level2").Preload("Level2.Level3").Find(&got).Error; err != nil {
+		panic(err)
+	}
+
+	if len(got) != 2 {
+		t.Fatalf("got %v items, expected 2", len(got))
+	}
+
+	if !reflect.DeepEqual(got[0], want) && !reflect.DeepEqual(got[1], want) {
+		t.Errorf("got %s; want array containing %s", toJSONString(got), toJSONString(want))
+	}
+
+	if !reflect.DeepEqual(got[0], want2) && !reflect.DeepEqual(got[1], want2) {
+		t.Errorf("got %s; want array containing %s", toJSONString(got), toJSONString(want2))
+	}
+}
+
 func toJSONString(v interface{}) []byte {
 	r, _ := json.MarshalIndent(v, "", "  ")
 	return r