From 26128548a5b317e3d61049bdd157c0efd7a3f775 Mon Sep 17 00:00:00 2001
From: Kyle Havlovitz <kylehav@gmail.com>
Date: Wed, 19 Apr 2023 10:23:38 -0700
Subject: [PATCH] Avoid decoding nil pointer in map walker (#17048)

---
 .changelog/17048.txt   |  3 +++
 lib/map_walker.go      |  2 +-
 lib/map_walker_test.go | 10 ++++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/17048.txt

diff --git a/.changelog/17048.txt b/.changelog/17048.txt
new file mode 100644
index 000000000..74f31c7ce
--- /dev/null
+++ b/.changelog/17048.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+Fix an bug where decoding some Config structs with unset pointer fields could fail with `reflect: call of reflect.Value.Type on zero Value`. 
+```
diff --git a/lib/map_walker.go b/lib/map_walker.go
index 8a0aeaf55..3e8cec77c 100644
--- a/lib/map_walker.go
+++ b/lib/map_walker.go
@@ -113,7 +113,7 @@ func (w *mapWalker) MapElem(m, k, v reflect.Value) error {
 		return nil
 	}
 
-	if inner := v.Elem(); inner.Type() == typMapIfaceIface {
+	if inner := v.Elem(); inner.IsValid() && inner.Type() == typMapIfaceIface {
 		// map[interface{}]interface{}, attempt to weakly decode into string keys
 		var target map[string]interface{}
 		if err := mapstructure.WeakDecode(v.Interface(), &target); err != nil {
diff --git a/lib/map_walker_test.go b/lib/map_walker_test.go
index b4d13bcca..2a3b4c189 100644
--- a/lib/map_walker_test.go
+++ b/lib/map_walker_test.go
@@ -41,6 +41,16 @@ func TestMapWalk(t *testing.T) {
 			},
 			unexpected: true,
 		},
+		// ensure we don't panic from trying to call reflect.Value.Type
+		// on a nil pointer
+		"nil pointer": {
+			input: map[string]interface{}{
+				"foo": nil,
+			},
+			expected: map[string]interface{}{
+				"foo": nil,
+			},
+		},
 		// ensure nested maps get processed correctly
 		"nested": {
 			input: map[string]interface{}{