code: def series2seq(
      ts: Optional[Union[TimeSeries, Sequence[TimeSeries]]]
  ) -> Optional[Sequence[TimeSeries]]:
      """If `ts` is a single TimeSeries, return it as a list of a single TimeSeries.
  
      Parameters
      ----------
      ts
          None, a single TimeSeries, or a sequence of TimeSeries
  
      Returns
      -------
          `ts` if `ts` is not a TimeSeries, else `[ts]`
  
      """
      return [ts] if isinstance(ts, TimeSeries) else ts
  
imports: from enum import Enum
  from functools import wraps
  from inspect import Parameter, getcallargs, signature
  from typing import Callable, Iterator, List, Optional, Sequence, Tuple, TypeVar, Union
  import pandas
  from joblib import Parallel, delayed
  from tqdm import tqdm
  from tqdm.notebook import tqdm
  from darts import TimeSeries
  from darts.logging import get_logger, raise_if_not, raise_log
  from darts.utils.timeseries_generation import generate_index
label_desc: Use image node_id 6 for calling a global function with example usage: series2seq(ts) and returns: unknown