Fix a frozen string error in lib/gitlab/utils.rb

Signed-off-by: Rémy Coutable <remy@rymai.me>

changelogs/unreleased/55116-runtimeerror-can-t-modify-frozen-string.yml

@@ -0,0 +1,5 @@
+---
+title: Fix a frozen string error in lib/gitlab/utils.rb
+merge_request: 23690
+author:
+type: fixed

lib/gitlab/utils.rb

@@ -60,7 +60,7 @@ module Gitlab
 
     # Converts newlines into HTML line break elements
     def nlbr(str)
-      ActionView::Base.full_sanitizer.sanitize(str, tags: []).gsub(/\r?\n/, '<br>').html_safe
+      ActionView::Base.full_sanitizer.sanitize(+str, tags: []).gsub(/\r?\n/, '<br>').html_safe
     end
 
     def remove_line_breaks(str)

spec/lib/gitlab/utils_spec.rb

@@ -44,6 +44,12 @@ describe Gitlab::Utils do
     end
   end
 
+  describe '.nlbr' do
+    it 'replaces new lines with <br>' do
+      expect(described_class.nlbr("<b>hello</b>\n<i>world</i>".freeze)).to eq("hello<br>world")
+    end
+  end
+
   describe '.remove_line_breaks' do
     using RSpec::Parameterized::TableSyntax