code: def test_get_result_none_predecessor():
      step = Step(None, "X", None, None, {})
      step.buffer = pd.DataFrame([1, 2, 3])
      result = step.get_result(True, "transform", ["transform"], {})
  
      pd.testing.assert_frame_equal(
          result.result, pd.DataFrame([1, 2, 3])
      )
      assert result.mode == ""
  
file_path: sktime/sktime/pipeline/tests/test_step.py
imports: from unittest.mock import MagicMock
  import pandas
  import pytest
  from sktime.forecasting.naive import NaiveForecaster
  from sktime.pipeline.step import Step, StepResult
  from sktime.transformations.series.exponent import ExponentTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_result_none_predecessor() without return types