message: Shared empty set instance to maybe allocate less.
diff: import { WishListRoll, DimWishList, WishListAndInfo } from './types';
  import _ from 'lodash';
  +const EMPTY_NUMBER_SET = new Set<number>();
  +
  /* Utilities for reading a wishlist file */
  /**
  @@ -21,7 +23,7 @@ function expectedMatchResultsLength(matchResults: RegExpMatchArray): boolean {
  function getPerks(matchResults: RegExpMatchArray): Set<number> {
  if (matchResults[2] === undefined) {
  - return new Set();
  + return EMPTY_NUMBER_SET;
  }
  return new Set(
  