code: def test_none_predictions(self):
      aggregator = AggregatePredictions()
  
      with warnings.catch_warnings(record=True) as w:
          state_1 = {torchbearer.Y_PRED: [None]}
  
          aggregator.on_step_validation(state_1)
          aggregator.on_step_validation(state_1)
  
          self.assertTrue(
              list(aggregator.predictions_list) == [[None], [None]]
          )
  
          aggregator.on_end_validation(state_1)
          self.assertTrue(
              state_1[torchbearer.FINAL_PREDICTIONS] == [[None], [None]]
          )
  
file_path: torchbearer/tests/callbacks/test_aggregate_predictions.py
imports: from unittest import TestCase
  import torch
  import warnings
  from torchbearer.callbacks import AggregatePredictions
  import torchbearer
label_desc: Use image node_id 3 for calling the TestAggregatePredictions obj's underlying member method code with example usage: obj.test_none_predictions() without return types