From 321039338cea661ec846d2855beb42c6728c27c4 Mon Sep 17 00:00:00 2001
From: team-humaki <team@humaki.com>
Date: Fri, 11 Sep 2026 10:52:04 -0700
Subject: [PATCH] MapTo: return error for nil struct pointer instead of panic

Calling MapTo(&cfg) when cfg is a nil *T used to panic in mapToField.
Return a clear error instead (#369).

Fixes #369
---
 struct.go      |  8 ++++++++
 struct_test.go | 14 ++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/struct.go b/struct.go
index 819a6e5..d70e11e 100644
--- a/struct.go
+++ b/struct.go
@@ -381,6 +381,9 @@ func (s *Section) mapToSlice(secName string, val reflect.Value, isStrict bool) (
 func (s *Section) mapTo(v interface{}, isStrict bool) error {
 	typ := reflect.TypeOf(v)
 	val := reflect.ValueOf(v)
+	if typ == nil || !val.IsValid() {
+		return errors.New("nil pointer to a struct")
+	}
 	if typ.Kind() == reflect.Pointer {
 		typ = typ.Elem()
 		val = val.Elem()
@@ -388,6 +391,11 @@ func (s *Section) mapTo(v interface{}, isStrict bool) error {
 		return errors.New("not a pointer to a struct")
 	}
 
+	// MapTo(&cfg) where cfg is a nil *T used to panic in mapToField (#369).
+	if !val.IsValid() || (val.Kind() == reflect.Pointer && val.IsNil()) {
+		return errors.New("nil pointer to a struct")
+	}
+
 	if typ.Kind() == reflect.Slice {
 		newField, err := s.mapToSlice(s.name, val, isStrict)
 		if err != nil {
diff --git a/struct_test.go b/struct_test.go
index ad6ad04..997f8d1 100644
--- a/struct_test.go
+++ b/struct_test.go
@@ -910,3 +910,17 @@ Title = Consultant Engineer
 		)
 	})
 }
+
+func TestMapToNilStructPointer(t *testing.T) {
+	t.Run("nil pointer to struct", func(t *testing.T) {
+		type Config struct {
+			User string `ini:"user"`
+			Pass string `ini:"pass"`
+		}
+		var cfg *Config
+		f, err := Load([]byte("user = alice\npass = secret\n"))
+		require.NoError(t, err)
+		err = f.MapTo(&cfg)
+		assert.EqualError(t, err, "nil pointer to a struct")
+	})
+}