Fix line commenting for the initial commit20895-inline-comments-for-first-commit

The initial commit doesn't have a parent, so explicitly pass the blank
SHA and handle that when calculating the position.

1 files changed, 9 insertions, 3 deletions

diff --git a/lib/gitlab/diff/position.rb b/lib/gitlab/diff/position.rb
index 2fdcf8d7838..088e105d771 100644
--- a/lib/gitlab/diff/position.rb
+++ b/lib/gitlab/diff/position.rb
@@ -139,13 +139,19 @@ module Gitlab
       private
 
       def find_diff_file(repository)
-        diffs = Gitlab::Git::Compare.new(
+        compare = Gitlab::Git::Compare.new(
           repository.raw_repository,
           start_sha,
           head_sha
-        ).diffs(paths: paths)
+        )
+
+        # We're at the initial commit, so just get that.
+        if start_sha == Gitlab::Git::BLANK_SHA && compare.commits.empty?
+          compare = Gitlab::Git::Commit.find(repository.raw_repository, head_sha)
+        end
+
+        diff = compare.diffs(paths: paths).first
 
-        diff = diffs.first
         return unless diff
 
         Gitlab::Diff::File.new(diff, repository: repository, diff_refs: diff_refs)