Don't allow resolving invalid conflicts

An MR can only be resolved in the UI if:
- It has conflicts.
- It has valid diff_refs (in other words, it supports new diff notes).
- It has no conflicts with one side missing.
- It has no conflicts in binary files.
- It has no conflicts in files too large to display.
- It has no conflicts containing invalid conflict markers.

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/gitlab/conflict/file.rb b/lib/gitlab/conflict/file.rb
index 1d63aec6903..cdbb63f626f 100644
--- a/lib/gitlab/conflict/file.rb
+++ b/lib/gitlab/conflict/file.rb
@@ -69,9 +69,9 @@ module Gitlab
 
         lines.each do |line|
           if line.type == 'old'
-            line.rich_text = their_highlight[line.old_line - 1].html_safe
+            line.rich_text = their_highlight[line.old_line - 1].try(:html_safe)
           else
-            line.rich_text = our_highlight[line.new_line - 1].html_safe
+            line.rich_text = our_highlight[line.new_line - 1].try(:html_safe)
           end
         end
       end