Handle corner case in squad_lib when best_non_null_entry is None.

PiperOrigin-RevId: 312193729

official/nlp/data/squad_lib.py

@@ -36,6 +36,17 @@ class SquadExample(object):
   """A single training/test example for simple sequence classification.
 
   For examples without an answer, the start and end position are -1.
+
+  Attributes:
+    qas_id: ID of the question-answer pair.
+    question_text: Original text for the question.
+    doc_tokens: The list of tokens in the context obtained by splitting
+      on whitespace only.
+    orig_answer_text: Original text for the answer.
+    start_position: Starting index of the answer in `doc_tokens`.
+    end_position: Ending index of the answer in `doc_tokens`.
+    is_impossible: Whether the question is impossible to answer given the
+      context. Only used in SQuAD 2.0.
   """
 
   def __init__(self,
@@ -695,6 +706,7 @@ def postprocess_output(all_examples,
     else:
       # pytype: disable=attribute-error
       # predict "" iff the null score - the score of best non-null > threshold
+      if best_non_null_entry is not None:
         score_diff = score_null - best_non_null_entry.start_logit - (
             best_non_null_entry.end_logit)
         scores_diff_json[example.qas_id] = score_diff
@@ -702,6 +714,10 @@ def postprocess_output(all_examples,
           all_predictions[example.qas_id] = ""
         else:
           all_predictions[example.qas_id] = best_non_null_entry.text
+      else:
+        logging.warning("best_non_null_entry is None")
+        scores_diff_json[example.qas_id] = score_null
+        all_predictions[example.qas_id] = ""
       # pytype: enable=attribute-error
 
     all_nbest_json[example.qas_id] = nbest_json