code: def _maybe_nest_bare_single(items_by_key, parallel):
      
      if (parallel == "multi-parallel" and
            (sum([1 for x in items_by_key.values() if not _is_nested_item(x)]) >=
             sum([1 for x in items_by_key.values() if _is_nested_item(x)]))):
          out = {}
          for k, v in items_by_key.items():
              out[k] = [v]
          return out
      else:
          return items_by_key
docs: Nest single inputs to avoid confusing single items and lists like files.