class_docstr: A `ListField` is a list of other fields.  You would use this to represent, e.g., a list of
  answer options that are themselves `TextFields`.
  
  This field will get converted into a tensor that has one more mode than the items in the list.
  If this is a list of `TextFields` that have shape (num_words, num_characters), this
  `ListField` will output a tensor of shape (num_sentences, num_words, num_characters).
  
  # Parameters
  
  field_list : `List[Field]`
      A list of `Field` objects to be concatenated into a single input tensor.  All of the
      contained `Field` objects must be of the same type.
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code: def empty_field(self):
      # Our "empty" list field will actually have a single field in the list, so that we can
      # correctly construct nested lists.  For example, if we have a type that is
      # `ListField[ListField[LabelField]]`, we need the top-level `ListField` to know to
      # construct a `ListField[LabelField]` when it's padding, and the nested `ListField` needs
      # to know that it's empty objects are `LabelFields`.  Having an "empty" list actually have
      # length one makes this all work out, and we'll always be padding to at least length 1,
      # anyway.
      return ListField([self.field_list[0].empty_field()])
  
file_path: allennlp/allennlp/data/fields/list_field.py
imports: from typing import Dict, List, Iterator, Sequence, Any
  from allennlp.data.fields.field import DataArray, Field
  from allennlp.data.vocabulary import Vocabulary
  from allennlp.data.fields.sequence_field import SequenceField
  from allennlp.common.util import pad_sequence_to_length
label_desc: Use image node_id 10 for calling the ListField obj's underlying member method code with example usage: obj.empty_field() and returns: ListField