From 28156a9952da525cc19b27a2eec926f04cae5d92 Mon Sep 17 00:00:00 2001
From: cuom1999 <lephuocdinh99@gmail.com>
Date: Tue, 26 Mar 2024 20:23:47 -0500
Subject: [PATCH] Fix type

---
 judge/ml/collab_filter.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/judge/ml/collab_filter.py b/judge/ml/collab_filter.py
index 0bdafa85..105a5341 100644
--- a/judge/ml/collab_filter.py
+++ b/judge/ml/collab_filter.py
@@ -71,7 +71,7 @@ def user_recommendations(self, user_id, problems, measure=DOT, limit=None):
     def problem_neighbors(self, problem, problemset, measure=DOT, limit=None):
         pid = problem.id
         if pid not in self.problem_embeddings:
-            return None
+            return []
         embedding = self.problem_embeddings[pid]
         scores = self.compute_scores(embedding, self.problem_embeddings, measure)
         res = []