selectOneMenu simple question...

Hi guys,
i'm a question for you.I'm using for the first time a selectonemenu tag
in my JSF application and i've this error

javax.servlet.ServletException: javax.servlet.jsp.JspException: Value
binding '#{user.teams}'of UISelectItems with component-path
{Component-Path : [Class: javax.faces.component.UIViewRoot,ViewId:
/Login.jsp][Class: javax.faces.component.html.HtmlForm,Id: _id1][Class:
javax.faces.component.html.HtmlPanelGrid,Id: _id2][Class:
javax.faces.component.html.HtmlPanelGrid,Id: _id4][Class:
javax.faces.component.html.HtmlSelectOneMenu,Id: selectTeam][Class:
javax.faces.component.UISelectItems,Id: _id19]} does not reference an
Object of type SelectItem, SelectItem[], Collection or Map but of type
: null
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:821)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:758)
    org.apache.jsp.Login_jsp._jspService(Login_jsp.java:114)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    com.sun.faces.context.ExternalContextImpl.dispatch(ExternalContextImpl.java:322)
    com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:130)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:87)
    com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:117)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:198)
    org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:670)
    org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:637)
    org.apache.jsp.index_jsp._jspService(index_jsp.java:43)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

root cause

java.lang.IllegalArgumentException: Value binding '#{user.teams}'of
UISelectItems with component-path {Component-Path : [Class:
javax.faces.component.UIViewRoot,ViewId: /Login.jsp][Class:
javax.faces.component.html.HtmlForm,Id: _id1][Class:
javax.faces.component.html.HtmlPanelGrid,Id: _id2][Class:
javax.faces.component.html.HtmlPanelGrid,Id: _id4][Class:
javax.faces.component.html.HtmlSelectOneMenu,Id: selectTeam][Class:
javax.faces.component.UISelectItems,Id: _id19]} does not reference an
Object of type SelectItem, SelectItem[], Collection or Map but of type
: null
    org.apache.myfaces.shared_impl.util.SelectItemsIterator.hasNext(SelectItemsIterator.java:141)
    org.apache.myfaces.shared_impl.renderkit.RendererUtils.internalGetSelectItemList(RendererUtils.java:477)
    org.apache.myfaces.shared_impl.renderkit.RendererUtils.getSelectItemList(RendererUtils.java:453)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlRendererUtils.internalRenderSelect(HtmlRendererUtils.java:277)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlRendererUtils.renderMenu(HtmlRendererUtils.java:251)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlMenuRendererBase.encodeEnd(HtmlMenuRendererBase.java:54)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:720)
    org.apache.myfaces.shared_impl.renderkit.RendererUtils.renderChild(RendererUtils.java:442)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlGridRendererBase.renderChildren(HtmlGridRendererBase.java:216)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlGridRendererBase.encodeEnd(HtmlGridRendererBase.java:98)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:720)
    org.apache.myfaces.shared_impl.renderkit.RendererUtils.renderChild(RendererUtils.java:442)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlGridRendererBase.renderChildren(HtmlGridRendererBase.java:216)
    org.apache.myfaces.shared_impl.renderkit.html.HtmlGridRendererBase.encodeEnd(HtmlGridRendererBase.java:98)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:720)
    javax.faces.webapp.UIComponentTag.encodeEnd(UIComponentTag.java:623)
    javax.faces.webapp.UIComponentTag.doEndTag(UIComponentTag.java:546)
    com.sun.faces.taglib.html_basic.PanelGridTag.doEndTag(PanelGridTag.java:460)
    org.apache.jsp.Login_jsp._jspx_meth_h_panelGrid_0(Login_jsp.java:249)
    org.apache.jsp.Login_jsp._jspx_meth_h_form_0(Login_jsp.java:210)
    org.apache.jsp.Login_jsp._jspx_meth_f_view_0(Login_jsp.java:162)
    org.apache.jsp.Login_jsp._jspService(Login_jsp.java:105)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    com.sun.faces.context.ExternalContextImpl.dispatch(ExternalContextImpl.java:322)
    com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:130)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:87)
    com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:117)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:198)
    org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:670)
    org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:637)
    org.apache.jsp.index_jsp._jspService(index_jsp.java:43)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

In my Login.jsp i have this selectoneMenu tag inside a form

<h:selectOneMenu id="selectTeam"
  value="#{authenticationBean.teamName}">
   <f:selectItems
   value="#{user.teams}" />
        </h:selectOneMenu>

where authenticationBean authenticates login and user.teams cames from
bean User where

private List<SelectItem> teams;
public List<SelectItem> getTeams() {
        return teams;
    }

    public void setTeams(List<SelectItem> teams) {
        this.teams = teams;
    }
public List<SelectItem> teamList() throws SQLException {
        try{
            DataSource dataSource=Singleton.getInstance().getDataSource();
            Connection conn=dataSource.getConnection();
            Statement stmt = conn.createStatement();
            ResultSet rst = stmt
                .executeQuery("select * from researchteam order by
teamname");
            List<SelectItem> teams = new ArrayList();
            while (rst.next())
                teams.add(new
SelectItem(rst.getString("teamname"),rst.getString("teamname")));
            rst.close();
            conn.close();
        }
        catch(Exception e){};
        return teams;
    }

Can you help me to find the error?
Thanks...