Add map test case

fmutils.go

@@ -186,9 +186,8 @@ func (mask NestedMask) overwrite(srcRft, destRft protoreflect.Message) {
 			srcMap.Range(func(mk protoreflect.MapKey, mv protoreflect.Value) bool {
 				if mi, ok := submask[mk.String()]; ok {
 					if i, ok := mv.Interface().(protoreflect.Message); ok && len(mi) > 0 {
-						destVal := protoreflect.ValueOf(mv)
-						destMap.Set(mk, destVal)
-						mi.overwrite(i, destVal.Message())
+						destMap.Set(mk, mv)
+						mi.overwrite(i, mv.Message())
 					} else {
 						destMap.Set(mk, mv)
 					}

fmutils_test.go

@@ -883,6 +883,47 @@ func TestOverwrite(t *testing.T) {
 				},
 			},
 		},
+		{
+			name:  "overwrite map with message values",
+			paths: []string{"attributes.src1.tags", "attributes.src2.tags"},
+			src: &testproto.Profile{
+				User: nil,
+				Attributes: map[string]*testproto.Attribute{
+					"src1": {
+						Tags: map[string]string{"key1": "value1", "key2": "value2"},
+					},
+					"src2": {
+						Tags: map[string]string{"key3": "value3"},
+					},
+				},
+			},
+			dest: &testproto.Profile{
+				User: &testproto.User{
+					Name: "name",
+				},
+				Attributes: map[string]*testproto.Attribute{
+					"dest1": {
+						Tags: map[string]string{"key4": "value5"},
+					},
+				},
+			},
+			want: &testproto.Profile{
+				User: &testproto.User{
+					Name: "name",
+				},
+				Attributes: map[string]*testproto.Attribute{
+					"src1": {
+						Tags: map[string]string{"key1": "value1", "key2": "value2"},
+					},
+					"src2": {
+						Tags: map[string]string{"key3": "value3"},
+					},
+					"dest1": {
+						Tags: map[string]string{"key4": "value5"},
+					},
+				},
+			},
+		},
 		{
 			name:  "overwrite repeated message fields",
 			paths: []string{"gallery.path"},