static <T> Set<T> findMissing(Set<T> toFind, Set<T> toSearch) {
        Set<T> ret = new LinkedHashSet<>();
        for (T toFindItem: toFind) {
            if (!toSearch.contains(toFindItem)) {
                ret.add(toFindItem);
            }
        }
        return ret;
    }
Return missing items which are expected to be in a particular set, but which are not.

@param toFind    The items to look for.
@param toSearch  The set of items to search.
@return          Empty set if all items were found; some of the missing ones in a set, if not.
clients/src/main/java/org/apache/kafka/clients/FetchSessionHandler.java