docs: public static Map<Integer, List<TagWrapper>> getCategoryMappingFromTagList(final Collection<TagWrapper> tags) {
          final HashMap<Integer, List<TagWrapper>> mapping = new HashMap<Integer, List<TagWrapper>>();
          for (final TagWrapper tag : tags) {
              final List<CategoryInTagWrapper> catList = tag.getCategories().getItems();
              if (catList != null) {
                  for (final CategoryInTagWrapper cat : catList) {
                      if (!mapping.containsKey(cat.getId())) {
                          mapping.put(cat.getId(), new ArrayList<TagWrapper>());
                      }
                      mapping.get(cat.getId()).add(tag);
                  }
              }
          }
          return mapping;
      }