class_docstr: Wrapper to load a custom dataset. Please review the `tutorial <tutorials/CustomDataset>` to get started.
code: def check_ts_for_metadata(self, ts, col):
      if col not in ts:
          if col == "trainval":
              ts[col] = ts.index <= ts.index[0] + (
                  ts.index[-1] - ts.index[0]
              ) * (1 - self.test_frac)
          else:
              raise ValueError(
                  f"Expected time series {ts} to have metadata column {col}. Columns: {ts.columns}"
              )
      return ts
  
file_path: merlion/ts_datasets/ts_datasets/forecast/custom.py
imports: import glob
  import os
  import pandas
  from ts_datasets.base import BaseDataset
label_desc: Use image node_id 3 for calling the CustomDataset obj's underlying member method code with example usage: obj.check_ts_for_metadata(ts, col) and returns: ts