Update scores/sisdr.py

scores/sisdr.py

@@ -12,7 +12,7 @@ class SISDR(ScoreBasis):
         # and one estimate.
         # see original code here: https://github.com/sigsep/bsseval/issues/3#issuecomment-494995846
         if len(audios) != 2:
-            raise ValueError('PESQ needs a reference and a test signals.')
+            return None
         eps = np.finfo(audios[0].dtype).eps
         reference = audios[1].reshape(audios[1].size, 1)
         estimate = audios[0].reshape(audios[0].size, 1)