code: function set(cache, keys, value) {
    if (keys.length === 0) {
      cache.set(sentinel, value);
    } else {
      const [key, ...restKeys] = keys;
      let nestedCache = cache.get(key);
      if (!nestedCache) {
        nestedCache = new Map();
        cache.set(key, nestedCache);
      }
      set(nestedCache, restKeys, value);
    }
    return value;
  }
docs: Set a value in the given cache Map, creating a new nested Map
  (or using an existing Map) for each value in `keys`.
  The innermost Map will have `map.get(sentinel) === value`.
  @param {Map}        cache The base Map for which to set a value
  @param {Array<Any>} keys  An array of keys for which new nested Maps will be created/used
  @param {Any}        value The value to set in the cache