code: def doc_to_target(self, doc):
      answer_list = doc["answers"]["text"]
      if len(answer_list) > 0:
          answer = answer_list[0]
      else:
          answer = "unanswerable"
      return " " + answer
  
imports: import datasets
  from math import exp
  from lm_eval.base import rf, Task
  from functools import partial
  from packaging import version
label_desc: Use image node_id 9 for calling the SQuAD2 obj's underlying member method code with example usage: obj.doc_to_target(doc) and returns: unknown