code: def test_training_step_none_batches(tmpdir):
      """Tests correctness when the train dataloader gives None for some steps."""
  
      class TestModel(BoringModel):
          def __init__(self):
              super().__init__()
              self.counter = 0
  
          def collate_none_when_even(self, batch):
              result = (
                  None
                  if self.counter % 2 == 0
                  else default_collate(batch)
              )
              self.counter += 1
              return result
  
          def train_dataloader(self):
              return DataLoader(
                  RandomDataset(32, 4),
                  collate_fn=self.collate_none_when_even,
              )
  
          def on_train_batch_end(self, outputs, batch, batch_idx):
              if batch_idx % 2 == 0:
                  assert outputs is None
              else:
                  assert outputs
  
      model = TestModel()
      trainer = Trainer(
          default_root_dir=tmpdir,
          limit_val_batches=1,
          max_epochs=4,
          enable_model_summary=False,
          logger=False,
          enable_checkpointing=False,
      )
  
      with pytest.warns(
          UserWarning, match=r".*train_dataloader yielded None.*"
      ):
          trainer.fit(model)
  
file_path: pytorch-lightning/tests/tests_pytorch/loops/test_training_loop_flow_scalar.py
imports: import pytest
  from lightning.pytorch import Trainer
  from lightning.pytorch.core.module import LightningModule
  from lightning.pytorch.demos.boring_classes import BoringModel, RandomDataset
  from lightning.pytorch.loops.optimization.automatic import Closure
  from lightning.pytorch.trainer.states import RunningStage
  from lightning_utilities.test.warning import no_warning_call
  from torch import Tensor
  from torch.utils.data import DataLoader
  from torch.utils.data._utils.collate import default_collate
  from tests_pytorch.helpers.deterministic_model import DeterministicModel
label_desc: Use image node_id 6 for calling a global function with example usage: test_training_step_none_batches(tmpdir) and returns: result, DataLoader