From 67bef15e53a77b6f1557fdd0efa65f3e916c20df Mon Sep 17 00:00:00 2001
From: Yamagishi Kazutoshi <ykzts@desire.sh>
Date: Tue, 24 Sep 2019 00:25:10 +0900
Subject: [PATCH] Add fallback section ID with ToC (#11941)

---
 app/lib/toc_generator.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/app/lib/toc_generator.rb b/app/lib/toc_generator.rb
index 351675a5c..0c8f766ca 100644
--- a/app/lib/toc_generator.rb
+++ b/app/lib/toc_generator.rb
@@ -45,7 +45,7 @@ class TOCGenerator
     parsed_html.traverse do |node|
       next unless TARGET_ELEMENTS.include?(node.name)
 
-      anchor = node['id'] || node.text.parameterize
+      anchor = node['id'] || node.text.parameterize.presence || 'sec'
       @slugs[anchor] += 1
       anchor = "#{anchor}-#{@slugs[anchor]}" if @slugs[anchor] > 1