code: def test_encode_batch_with_example_with_empty_first_elem():
      features = Features(
          {
              "x": Sequence(Sequence(ClassLabel(names=["a", "b"]))),
          }
      )
      encoded_batch = features.encode_batch(
          {
              "x": [
                  [["a"], ["b"]],
                  [[], ["b"]],
              ]
          }
      )
      assert encoded_batch == {"x": [[[0], [1]], [[], [1]]]}
  
imports: import datetime
  from unittest import TestCase
  from unittest.mock import patch
  import numpy
  import pandas
  import pyarrow
  import pytest
  from datasets import Array2D
  from datasets.arrow_dataset import Dataset
  from datasets.features import Audio, ClassLabel, Features, Image, Sequence, Value
  from datasets.features.features import _arrow_to_datasets_dtype, _cast_to_python_objects, cast_to_python_objects, encode_nested_example, generate_from_dict, string_to_arrow
  from datasets.features.translation import Translation, TranslationVariableLanguages
  from datasets.info import DatasetInfo
  from datasets.utils.py_utils import asdict
  from ..utils import require_jax, require_tf, require_torch
label_desc: Use image node_id 7 for calling a global function with example usage: test_encode_batch_with_example_with_empty_first_elem() without return types