Update scores/stoi.py

scores/stoi.py

@@ -10,7 +10,7 @@ class STOI(ScoreBasis):
     def windowed_scoring(self, audios, score_rate):
         from pystoi.stoi import stoi
         if len(audios) != 2:
-            raise ValueError('STOI needs a reference and a test signals.')
+            return None
 
         return stoi(audios[1], audios[0], score_rate, extended=False)