public static <C extends Collection<T>, T> Set<T> mutableSet(final C set) {
        return set != null
                ? new HashSet<>(set)
                : new HashSet<>();
    }
Returns a new {@link java.util.HashSet} instance. If set is not null, the new {@link java.util.HashSet} will
contain the contents of set, else it will be empty.
stroom-util-shared/src/main/java/stroom/util/shared/NullSafe.java