can not pre-set value for combo box

package fi.uwasa.netmes.zkossController;

import java.util.List;
import java.util.Map;

import org.zkoss.zk.ui.event.CreateEvent;
import org.zkoss.zk.ui.event.Event;
import org.zkoss.zkplus.databind.AnnotateDataBinder;
import org.zkoss.zul.Window;

import fi.uwasa.netmes.bean.Site;
import fi.uwasa.netmes.bean.User;
import fi.uwasa.netmes.util.SpringUtil;

public class EditUserController extends Window  {
	private static final long serialVersionUID = 1L;
	private AnnotateDataBinder binder;
	private User user;
	private Site selectedSite;
	 
	public Map<String, Object> getCreationArgsMap(Event event) {
		CreateEvent ce = (CreateEvent) event;
		return ce.getArg();
	}
	public void onCreate(Event event) throws Exception {
		binder = (AnnotateDataBinder) this.getVariable("binder", false);
		Map<String, Object> args = getCreationArgsMap(event);
		this.setUser((User) args.get("user"));
		selectedSite=SpringUtil.getSiteService().getSites().get(0);
		binder.loadAll();
	}
	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}
	public List<Site> getAvailableSites()  {
		
		
		return SpringUtil.getSiteService().getSites();
	}
	public Site getSelectedSite() {
		return selectedSite;
	}
	public void setSelectedSite(Site selectedSite) {
		this.selectedSite = selectedSite;
	}

	
}

<?page title="NetMES" contentType="text/html;charset=UTF-8"?>
<?init class="org.zkoss.zkplus.databind.AnnotateDataBinderInit" arg0="./editUserWin"?>

<window id="editUserWin" border="normal" title="Edit User" width="400px"
	height="350px" style="padding-top:30px"
	use="fi.uwasa.netmes.zkossController.EditUserController">
	<vbox style="padding-top:5%" width="100%" height="100%">
		<div align="center" style="float: center" >
			<grid width="100%" height="100%" >
				<rows>

					<row zclass="none" style="padding-top:5px">
						<div align="center" style="float: right">
							<label value="Email" id="lbEmail" />
						</div>
						<div align="center"
							style="float: left; padding-left:10px">
							<textbox id="tbEmail" value="@{editUserWin.selectedSite.name}"/>
						</div>
					</row>

				

					<row zclass="none" style="padding-top:5px">
						<div align="right" style="float: right">
							<label value="Site" id="lbSite" />
						</div>
						<div align="center"
							style="float: left; padding-left:10px">
							<combobox id="cbSite" model="@{editUserWin.availableSites}" selectedItem="@{editUserWin.selectedSite}">
								    <comboitem self="@{each=site}" label="@{site.name}" value="@{site}" />
							</combobox>
						</div>

					</row>

				</rows>
			</grid>
		</div>
	</vbox>
</window>