code: def test_list_field_can_handle_empty_index_fields(self):
      list_field = ListField(
          [self.index_field, self.index_field, self.empty_index_field]
      )
      list_field.index(self.vocab)
      tensor = list_field.as_tensor(list_field.get_padding_lengths())
      numpy.testing.assert_array_equal(
          tensor.detach().cpu().numpy(), numpy.array([[1], [1], [-1]])
      )
  
imports: from typing import Dict
  import numpy
  import torch
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data import Token, Vocabulary, Instance
  from allennlp.data.fields import TextField, LabelField, ListField, IndexField, SequenceLabelField
  from allennlp.data.token_indexers import SingleIdTokenIndexer, TokenCharactersIndexer
  from allennlp.data.data_loaders import SimpleDataLoader
  from allennlp.data.tokenizers import SpacyTokenizer
  from allennlp.models import Model
  from allennlp.modules import Embedding
  from allennlp.modules.text_field_embedders import BasicTextFieldEmbedder
label_desc: Use image node_id 4 for calling the TestListField obj's underlying member method code with example usage: obj.test_list_field_can_handle_empty_index_fields() without return types