code: public DocumentationBuilder apiListingsByResourceGroupName(Map<String, List<ApiListing>> apiListings) {
      nullToEmptyMultimap(apiListings).entrySet().stream().forEachOrdered(entry -> {
        List<ApiListing> list;
        if (this.apiListings.containsKey(entry.getKey())) {
          list = this.apiListings.get(entry.getKey());
          list.addAll(entry.getValue());
        } else {
          list = new ArrayList<>(entry.getValue());
          this.apiListings.put(entry.getKey(), list);
        }
        list.sort(byListingPosition());
      });
      return this;
    }
docs: Updates the map with new entries
  
  @param apiListings - entries to add to the existing documentation
  @return this