@Override
	public Set<String> toStrings(Set<SystemScope> scope) {
		if (scope == null) {
			return null;
		} else {
			return new LinkedHashSet<>(Collections2.filter(Collections2.transform(scope, systemScopeToString), Predicates.notNull()));
		}
	}
@Test
	public void toStrings() {

		// check null condition
		assertThat(service.toStrings(null), is(nullValue()));

		assertThat(service.toStrings(allScopes), equalTo(allScopeStrings));

		assertThat(service.toStrings(allScopesWithValue), equalTo(allScopeStringsWithValue));
	}