code: public KeePassFile enrichNodesWithIconData(KeePassFile keePassFile) {
          CustomIcons iconLibrary = keePassFile.getMeta().getCustomIcons();
          GroupZipper zipper = new GroupZipper(keePassFile);
          Iterator<Group> iter = zipper.iterator();
  
          while (iter.hasNext()) {
              Group group = iter.next();
  
              byte[] iconData = getIconData(group.getCustomIconUuid(), group.getIconId(), iconLibrary);
              Group groupWithIcon = new GroupBuilder(group).iconData(iconData).build();
              zipper.replace(groupWithIcon);
  
              enrichEntriesWithIcons(iconLibrary, group);
          }
  
          return zipper.close();
      }
docs: Iterates through all nodes of the given KeePass file and replace the
  nodes with enriched icon data nodes.
  
  @param keePassFile
  the KeePass file which should be iterated
  @return an enriched KeePass file