class_docstr: Store a mapping from keys to multiple values with minimal overhead.
  
  Avoids storing empty collections.
code: def get_all(self, k: K) -> list[V]:
      """ """
      existing = self._dict.get(k)
      if existing is None:
          return []
      elif isinstance(existing, set):
          return list(cast(set[V], existing))
      else:
          return [existing]
  
file_path: bokeh/src/bokeh/util/datatypes.py
imports: from __future__ import annotations
  import logging
  from typing import Generic, TypeVar, cast
label_desc: Use image node_id 3 for calling the MultiValuedDict obj's underlying member method code with example usage: obj.get_all(k) and returns: list, list, list