code: def test_combine_first_timestamp_bug_NaT():
      # GH28481
      frame = DataFrame([[pd.NaT, pd.NaT]], columns=["a", "b"])
      other = DataFrame(
          [[datetime(2020, 1, 1), datetime(2020, 1, 2)]],
          columns=["b", "c"],
      )
  
      result = frame.combine_first(other)
      expected = DataFrame(
          [[pd.NaT, datetime(2020, 1, 1), datetime(2020, 1, 2)]],
          columns=["a", "b", "c"],
      )
  
      tm.assert_frame_equal(result, expected)
  
imports: from datetime import datetime
  import numpy
  import pytest
  from pandas.core.dtypes.cast import find_common_type
  from pandas.core.dtypes.common import is_dtype_equal
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 2 for calling a global function with example usage: test_combine_first_timestamp_bug_NaT() without return types