From a2fc6f40b3bc305a53a3f05ad4b81d99ebb4aaf1 Mon Sep 17 00:00:00 2001
From: Masayoshi Mizutani <masayoshi.mizutani@dr-ubie.com>
Date: Mon, 26 Feb 2024 15:00:08 +0900
Subject: [PATCH] Add handling for nil interface in clone function

---
 clone.go      |  3 +++
 clone_test.go | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/clone.go b/clone.go
index 4e66523..2a7b91a 100644
--- a/clone.go
+++ b/clone.go
@@ -107,6 +107,9 @@ func (x *masq) clone(fieldName string, src reflect.Value, tag string) reflect.Va
 		return dst
 
 	case reflect.Interface:
+		if src.IsNil() {
+			return src
+		}
 		return x.clone(fieldName, src.Elem(), tag)
 
 	default:
diff --git a/clone_test.go b/clone_test.go
index 3bab049..677e320 100644
--- a/clone_test.go
+++ b/clone_test.go
@@ -316,3 +316,15 @@ func TestDirectUUID(t *testing.T) {
 
 	gt.S(t, buf.String()).Contains("stringer")
 }
+
+func TestNilInterface(t *testing.T) {
+	var buf bytes.Buffer
+	type myStruct struct {
+		Data interface{}
+	}
+	logger := slog.New(slog.NewJSONHandler(&buf, &slog.HandlerOptions{
+		ReplaceAttr: masq.New(),
+	}))
+	logger.Info("hello", slog.Any("test", myStruct{}))
+	gt.S(t, buf.String()).Contains("null")
+}