From 79f23264ef5eae0c77fd1c8cf67cb9c3dd2a6fa0 Mon Sep 17 00:00:00 2001
From: Virgil <virgil@lethean.io>
Date: Thu, 2 Apr 2026 07:33:52 +0000
Subject: [PATCH] fix(i18n): ignore nil handlers

Co-Authored-By: Virgil <virgil@lethean.io>
---
 handler.go   | 19 +++++++++++++++++++
 i18n_test.go | 37 +++++++++++++++++++++++++++++++++++++
 service.go   |  5 +++--
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/handler.go b/handler.go
index fe2ffd4..f564d27 100644
--- a/handler.go
+++ b/handler.go
@@ -259,6 +259,9 @@ func contextArgText(values any) string {
 // RunHandlerChain executes a chain of handlers for a key.
 func RunHandlerChain(handlers []KeyHandler, key string, args []any, fallback func() string) string {
 	for i, h := range handlers {
+		if h == nil {
+			continue
+		}
 		if h.Match(key) {
 			next := func() string {
 				remaining := handlers[i+1:]
@@ -273,6 +276,22 @@ func RunHandlerChain(handlers []KeyHandler, key string, args []any, fallback fun
 	return fallback()
 }
 
+func filterNilHandlers(handlers []KeyHandler) []KeyHandler {
+	if len(handlers) == 0 {
+		return nil
+	}
+	filtered := handlers[:0]
+	for _, h := range handlers {
+		if h != nil {
+			filtered = append(filtered, h)
+		}
+	}
+	if len(filtered) == 0 {
+		return nil
+	}
+	return filtered
+}
+
 var (
 	_ KeyHandler = LabelHandler{}
 	_ KeyHandler = ProgressHandler{}
diff --git a/i18n_test.go b/i18n_test.go
index 73f769f..68ab2ea 100644
--- a/i18n_test.go
+++ b/i18n_test.go
@@ -302,6 +302,20 @@ func TestAddHandler_Good_Variadic(t *testing.T) {
 	assert.IsType(t, ProgressHandler{}, handlers[1])
 }
 
+func TestAddHandler_Good_SkipsNil(t *testing.T) {
+	svc, err := New(WithHandlers())
+	require.NoError(t, err)
+	_ = Init()
+	SetDefault(svc)
+
+	var nilHandler KeyHandler
+	AddHandler(nilHandler, LabelHandler{})
+
+	handlers := svc.Handlers()
+	require.Len(t, handlers, 1)
+	assert.IsType(t, LabelHandler{}, handlers[0])
+}
+
 func TestPrependHandler_Good(t *testing.T) {
 	svc, err := New(WithHandlers()) // start with no handlers
 	require.NoError(t, err)
@@ -330,6 +344,20 @@ func TestPrependHandler_Good_Variadic(t *testing.T) {
 	assert.IsType(t, ProgressHandler{}, handlers[1])
 }
 
+func TestPrependHandler_Good_SkipsNil(t *testing.T) {
+	svc, err := New(WithHandlers())
+	require.NoError(t, err)
+	_ = Init()
+	SetDefault(svc)
+
+	var nilHandler KeyHandler
+	PrependHandler(nilHandler, LabelHandler{})
+
+	handlers := svc.Handlers()
+	require.Len(t, handlers, 1)
+	assert.IsType(t, LabelHandler{}, handlers[0])
+}
+
 func TestClearHandlers_Good(t *testing.T) {
 	svc, err := New()
 	require.NoError(t, err)
@@ -347,6 +375,15 @@ func TestClearHandlers_Good(t *testing.T) {
 	assert.Empty(t, svc.Handlers())
 }
 
+func TestNewWithHandlers_SkipsNil(t *testing.T) {
+	svc, err := New(WithHandlers(nil, LabelHandler{}))
+	require.NoError(t, err)
+
+	handlers := svc.Handlers()
+	require.Len(t, handlers, 1)
+	assert.IsType(t, LabelHandler{}, handlers[0])
+}
+
 // --- executeIntentTemplate ---
 
 func TestExecuteIntentTemplate_Good(t *testing.T) {
diff --git a/service.go b/service.go
index 09538c8..31c6978 100644
--- a/service.go
+++ b/service.go
@@ -56,7 +56,7 @@ func WithLocation(location string) Option {
 // WithHandlers sets custom handlers (replaces default handlers).
 func WithHandlers(handlers ...KeyHandler) Option {
 	return func(s *Service) {
-		s.handlers = append([]KeyHandler(nil), handlers...)
+		s.handlers = filterNilHandlers(append([]KeyHandler(nil), handlers...))
 	}
 }
 
@@ -339,12 +339,13 @@ func (s *Service) PluralCategory(n int) PluralCategory {
 func (s *Service) AddHandler(handlers ...KeyHandler) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	s.handlers = append(s.handlers, handlers...)
+	s.handlers = append(s.handlers, filterNilHandlers(handlers)...)
 }
 
 func (s *Service) PrependHandler(handlers ...KeyHandler) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	handlers = filterNilHandlers(handlers)
 	if len(handlers) == 0 {
 		return
 	}