getCollection (name) {
    const collection = this._collections[name]
    if (!collection) {
      throw utils.err(`${DOMAIN}#getCollection`, name)(404, 'collection')
    }
    return collection
  }
Return the {@link Collection} with the given name, if for some
reason you need a direct reference to the collection.

@method SimpleStore#getCollection
@param {string} name Name of the {@link Collection} to retrieve.
@returns {Collection}
@since 3.0.0
@throws {Error} Thrown if the specified {@link Collection} does not
exist.