code: def test_label_field_empty_field_works(self):
      label = LabelField("test")
      empty_label = label.empty_field()
      assert empty_label.label == -1
  
file_path: allennlp/tests/data/fields/label_field_test.py
imports: import logging
  import pytest
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data.fields import LabelField
  from allennlp.data import Vocabulary
label_desc: Use image node_id 5 for calling the TestLabelField obj's underlying member method code with example usage: obj.test_label_field_empty_field_works() without return types