From 05b45c35c8067b7c4a6c99fec64f124739d2e7fd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Erik=20Pedersen?=
 <bjorn.erik.pedersen@gmail.com>
Date: Wed, 20 Apr 2022 17:42:57 +0200
Subject: [PATCH] tpl/lang: Handle nil values in lang.Merge

---
 hugolib/pages_language_merge_test.go | 10 +++++++++-
 tpl/lang/lang.go                     |  7 +++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/hugolib/pages_language_merge_test.go b/hugolib/pages_language_merge_test.go
index 628abe8aa..55241d306 100644
--- a/hugolib/pages_language_merge_test.go
+++ b/hugolib/pages_language_merge_test.go
@@ -94,9 +94,9 @@ func TestMergeLanguagesTemplate(t *testing.T) {
 	b.WithTemplates("home.html", `
 {{ $pages := .Site.RegularPages }}
 {{ .Scratch.Set "pages" $pages }}
-{{ if eq .Language.Lang "nn" }}:
 {{ $enSite := index .Sites 0 }}
 {{ $frSite := index .Sites 1 }}
+{{ if eq .Language.Lang "nn" }}:
 {{ $nnBundle := .Site.GetPage "page" "bundle" }}
 {{ $enBundle := $enSite.GetPage "page" "bundle" }}
 {{ .Scratch.Set "pages" ($pages | lang.Merge $frSite.RegularPages| lang.Merge $enSite.RegularPages) }}
@@ -106,6 +106,10 @@ func TestMergeLanguagesTemplate(t *testing.T) {
 {{ $pages2 := .Scratch.Get "pages2" }}
 Pages1: {{ range $i, $p := $pages }}{{ add $i 1 }}: {{ .File.Path }} {{ .Language.Lang }} | {{ end }}
 Pages2: {{ range $i, $p := $pages2 }}{{ add $i 1 }}: {{ .Title }} {{ .Language.Lang }} | {{ end }}
+{{ $nil := resources.Get "asdfasdfasdf" }}
+Pages3: {{ $frSite.RegularPages | lang.Merge  $nil }}
+Pages4: {{  $nil | lang.Merge $frSite.RegularPages }}
+
 
 `,
 		"shortcodes/shortcode.html", "MyShort",
@@ -117,6 +121,10 @@ Pages2: {{ range $i, $p := $pages2 }}{{ add $i 1 }}: {{ .Title }} {{ .Language.L
 
 	b.AssertFileContent("public/nn/index.html", "Pages1: 1: p1.md en | 2: p2.nn.md nn | 3: p3.nn.md nn | 4: p4.md en | 5: p5.fr.md fr | 6: p6.nn.md nn | 7: p7.md en | 8: p8.md en | 9: p9.nn.md nn | 10: p10.fr.md fr | 11: p11.md en | 12: p12.nn.md nn | 13: p13.md en | 14: p14.md en | 15: p15.nn.md nn")
 	b.AssertFileContent("public/nn/index.html", "Pages2: 1: doc100 en | 2: doc101 nn | 3: doc102 nn | 4: doc103 en | 5: doc104 en | 6: doc105 en")
+	b.AssertFileContent("public/nn/index.html", `
+Pages3: Pages(3)
+Pages4: Pages(3)
+	`)
 }
 
 func newTestSiteForLanguageMerge(t testing.TB, count int) *sitesBuilder {
diff --git a/tpl/lang/lang.go b/tpl/lang/lang.go
index 33c4c093b..ee349bd1d 100644
--- a/tpl/lang/lang.go
+++ b/tpl/lang/lang.go
@@ -24,6 +24,7 @@ import (
 	translators "github.com/gohugoio/localescompressed"
 	"github.com/pkg/errors"
 
+	"github.com/gohugoio/hugo/common/hreflect"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/spf13/cast"
 )
@@ -250,6 +251,12 @@ type pagesLanguageMerger interface {
 
 // Merge creates a union of pages from two languages.
 func (ns *Namespace) Merge(p2, p1 any) (any, error) {
+	if !hreflect.IsTruthful(p1) {
+		return p2, nil
+	}
+	if !hreflect.IsTruthful(p2) {
+		return p1, nil
+	}
 	merger, ok := p1.(pagesLanguageMerger)
 	if !ok {
 		return nil, fmt.Errorf("language merge not supported for %T", p1)