code: def to_category(series: pd.Series, state: dict) -> pd.Series:
      hasnans = series.hasnans
      val = series.astype(str)
      if hasnans:
          val = val.replace("nan", np.nan)
          val = val.replace("<NA>", np.nan)
  
      return val.astype("string")
  
imports: import functools
  from typing import Callable, Dict
  import numpy
  import pandas
  from pandas.api import types
  from visions.backends.pandas.series_utils import series_handle_nulls
  from ydata_profiling.config import Settings
  from ydata_profiling.utils.versions import is_pandas_1
label_desc: Use image node_id 6 for calling a global function with example usage: to_category(series, state) and returns: val