code: public static @NotNull Collection<Object> notFound(@Nullable Collection<?> target, @NotNull Object... objects) {
      if (target == null) {
        return emptyList();
      }
      List<Object> notFound = newArrayList();
      for (Object o : objects) {
        if (!target.contains(o)) {
          notFound.add(o);
        }
      }
      return notFound;
    }
docs: Attempts to find the given objects in the given {@code Collection}, returning the ones that were not found.
  
  @param target  the given {@code Collection}.
  @param objects the elements to find in the given {@code Collection}.
  @return the elements that were not found in the given {@code Collection}.