code: def test_combine_first_duplicates_rows_for_nan_index_values():
      # GH39881
      df1 = DataFrame(
          {"x": [9, 10, 11]},
          index=MultiIndex.from_arrays(
              [[1, 2, 3], [np.nan, 5, 6]], names=["a", "b"]
          ),
      )
  
      df2 = DataFrame(
          {"y": [12, 13, 14]},
          index=MultiIndex.from_arrays(
              [[1, 2, 4], [np.nan, 5, 7]], names=["a", "b"]
          ),
      )
  
      expected = DataFrame(
          {
              "x": [9.0, 10.0, 11.0, np.nan],
              "y": [12.0, 13.0, np.nan, 14.0],
          },
          index=MultiIndex.from_arrays(
              [[1, 2, 3, 4], [np.nan, 5, 6, 7]], names=["a", "b"]
          ),
      )
      combined = df1.combine_first(df2)
      tm.assert_frame_equal(combined, 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 5 for calling a global function with example usage: test_combine_first_duplicates_rows_for_nan_index_values() without return types