Update contests_ranking_json.rb

Author: exKAZUu

app/controllers/concerns/api/contests_ranking_json.rb

@@ -60,7 +60,9 @@ def calculate_ranking_score(table)
       problem_id = submission.problem.id
       data_set_id = submission.data_set.id
       user_data = table[user_id]
-      data = table[user_id][:problems][problem_id][:data_sets][data_set_id]
+      if table[user_id] && table[user_id][:problems] && table[user_id][:problems][problem_id][:data_sets]
+        data = table[user_id][:problems][problem_id][:data_sets][data_set_id]
+      end
       update_ranking_score(submission, user_data, data) unless data[:correct]
     end
   end