code: def fillna(series_or_arr, missing_value=0.0):
      
  
      if pandas.notnull(missing_value):
          if isinstance(series_or_arr, (numpy.ndarray)):
              series_or_arr[numpy.isnan(series_or_arr)] = missing_value
          else:
              series_or_arr.fillna(missing_value, inplace=True)
  
      return series_or_arr
docs: Fill missing values in pandas objects and numpy arrays.
  
      Arguments
      ---------
      series_or_arr : pandas.Series, numpy.ndarray
          The numpy array or pandas series for which the missing values
          need to be replaced.
      missing_value : float, int, str
          The value to replace the missing value with. Default 0.0.
  
      Returns
      -------
      pandas.Series, numpy.ndarray
          The numpy array or pandas series with the missing values
          filled.