code: def test_none_to_nan(cls, dtype):
      a = cls._from_sequence(["a", None, "b"], dtype=dtype)
      assert a[1] is not None
      assert a[1] is na_val(a.dtype)
  
imports: import operator
  import numpy
  import pytest
  from pandas.compat.pyarrow import pa_version_under12p0
  from pandas.core.dtypes.common import is_dtype_equal
  import pandas
  import pandas._testing
  from pandas.core.arrays.string_arrow import ArrowStringArray, ArrowStringArrayNumpySemantics
label_desc: Use image node_id 5 for calling a global function with example usage: test_none_to_nan(cls, dtype) without return types