code: def _enforce_index_freq(item: pd.Series) -> pd.Series:
      """Enforce the frequency of a Series index using pd.infer_freq.
  
      Parameters
      ----------
      item : pd.Series
      Returns
      -------
      pd.Series
          Pandas series with the inferred frequency. If the frequency cannot be inferred
          it will stay None
      """
      if hasattr(item.index, "freq") and item.index.freq is None:
          if (
              len(item.index) > 2
          ):  # pandas.infer_freq errors out for length 1 or 2
              item.index.freq = pd.infer_freq(item.index)
      return item
  
imports: import itertools
  import numpy
  import pandas
  from sktime.datatypes._check import check_is_scitype, mtype
  from sktime.datatypes._convert import convert_to
  from sktime.utils.multiindex import flatten_multiindex
  from sktime.utils.parallel import parallelize
label_desc: Use image node_id 1 for calling a global function with example usage: _enforce_index_freq(item) and returns: item