code: function resolve (manager, resolveReducer, accumulator, reducer) {
    return BaseEntity.resolve(
      manager,
      resolveReducer,
      accumulator,
      reducer,
      reducer.entity
    )
  }
docs: Resolve an Entity Reducer, actual entity resolution is delegated
  to each Entity.resolve method
  @param {Object} manager
  @param {function} resolveReducer
  @param {Accumulator} accumulator
  @param {ReducerEntityId} reducer
  @returns {Promise<Accumulator>}