int towerId = message.getTowerId();
// sanity checks on the id
Client client = sender.getClient();
if (towerId <= 0) {
client.handleError(ErrorType.Error,
"Invalid tower id (tried to change strategy " + towerId + ")");
return;
} else if (towerId >= this.nextTowerId) {
client.handleError(ErrorType.Error,
"No such tower (tried to change strategy " + towerId + ")");