}
public List<String> associateClients(final Set<Client> clientMembersSet) {
final List<String> differences = new ArrayList<>();
for (final Client client : clientMembersSet) {
if (hasClientAsMember(client)) { throw new ClientExistInGroupException(client.getId(), getId()); }
this.clientMembers.add(client);
differences.add(client.getId().toString());
}
return differences;