FIX bug

app/views/compare/show.json.jbuilder

@@ -2,8 +2,12 @@ json.commits_count @compare_result['Commits']&.size
 json.commits @compare_result['Commits'], partial: 'pull_requests/commit', as: :commit
 
 json.diff do
-  json.files_count @compare_result['Diff']['NumFiles']
-  json.total_addition @compare_result['Diff']['TotalAddition']
-  json.total_deletion @compare_result['Diff']['TotalDeletion']
-  json.files @compare_result['Diff']['Files'], partial: 'pull_requests/diff_file', as: :file
+  if @compare_result['Diff'].blank?
+    json.nil!
+  else
+    json.files_count @compare_result['Diff']['NumFiles']
+    json.total_addition @compare_result['Diff']['TotalAddition']
+    json.total_deletion @compare_result['Diff']['TotalDeletion']
+    json.files @compare_result['Diff']['Files'], partial: 'pull_requests/diff_file', as: :file
+  end
 end