code: public Set<Type> getTypes(String path)
    {
      LinkedList<Type> types = new LinkedList<>();
      for (Reference reference : references)
      {
        if (Preconditions.checkNotNull(path).equals(reference.refResource))
        {
          types.add(reference.type);
        }
      }
      return Sets.immutableEnumSet(types);
    }
docs: Returns set (possibly multiple) types of refereences to the given resource
  
  @param path
  the path to a publication resource
  @return an immutable {@link EnumSet} containing the types of references to
  {@code path}.