Update config.generator.prefix

config.json

@@ -74,7 +74,7 @@
     "output_hidden_states": false,
     "output_scores": false,
     "pad_token_id": 1,
-    "prefix": null,
+    "prefix": " ",
     "problem_type": null,
     "pruned_heads": {},
     "remove_invalid_values": false,
@@ -125,7 +125,7 @@
   "n_docs": 5,
   "output_retrieved": false,
   "passages_path": null,
-  "prefix": " ",
+  "prefix": null,
   "question_encoder": {
     "_name_or_path": "zhiweitong/dpr-answer_encoder-single-nq-base",
     "add_cross_attention": false,