code: def test_fillna_null(null_obj, index_or_series_obj):
      # GH 11343
      obj = index_or_series_obj
      klass = type(obj)
  
      if not allow_na_ops(obj):
          pytest.skip(f"{klass} doesn't allow for NA operations")
      elif len(obj) < 1:
          pytest.skip("Test doesn't make sense on empty data")
      elif isinstance(obj, MultiIndex):
          pytest.skip(f"MultiIndex can't hold '{null_obj}'")
  
      values = obj._values
      fill_value = values[0]
      expected = values.copy()
      values[0:2] = null_obj
      expected[0:2] = fill_value
  
      expected = klass(expected)
      obj = klass(values)
  
      result = obj.fillna(fill_value)
      tm.assert_equal(result, expected)
  
      # check shallow_copied
      assert obj is not result
  
imports: import numpy
  import pytest
  from pandas import MultiIndex
  import pandas._testing
  from pandas.tests.base.common import allow_na_ops
label_desc: Use image node_id 2 for calling a global function with example usage: test_fillna_null(null_obj, index_or_series_obj) without return types