code: def get_single_series(
      ts: Optional[Union[TimeSeries, Sequence[TimeSeries]]]
  ) -> Optional[TimeSeries]:
      """Returns a single (first) TimeSeries or `None` from `ts`. Returns `ts` if  `ts` is a TimeSeries, `ts[0]` if
      `ts` is a Sequence of TimeSeries. Otherwise, returns `None`.
  
      Parameters
      ----------
      ts
          None, a single TimeSeries, or a sequence of TimeSeries.
  
      Returns
      -------
          `ts` if  `ts` is a TimeSeries, `ts[0]` if `ts` is a Sequence of TimeSeries. Otherwise, returns `None`
  
      """
      if isinstance(ts, TimeSeries) or ts is None:
          return ts
      else:
          return ts[0]
  
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 11 for calling a global function with example usage: get_single_series(ts) and returns: ts, ts