Add a safer use_sem accessor method in predict.py

combo/predict.py

@@ -150,7 +150,7 @@ class COMBO(PredictorModule):
         if self.without_sentence_embedding:
             outputs.sentence_embedding = []
         if self.line_to_conllu:
-            return sentence2conllu(outputs, keep_semrel=self.dataset_reader.use_sem).serialize()
+            return sentence2conllu(outputs, keep_semrel=getattr(self.dataset_reader, 'use_sem', False)).serialize()
         else:
             return outputs.to_json()