JSF - richfaces javax.servlet.ServletException

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:f="http://java.sun.com/jsf/core"
      xmlns:a4j="http://richfaces.org/a4j"
      xmlns:rich="http://richfaces.org/rich">


		<h:inputText id="id" value="#{oper.operador.id}"/><br></br>
		<h:inputText id="teste" value="#{oper.operador.nome}"/>
		<richfaces:suggestionbox	
			width="150"
			height="150"
			minChars="3"
			suggestionAction="#{oper.autocomplete}"
			var="op"
			id="testasuggestion"
			for="teste">
			<h:column>
				<h:outputText value="#{op.nome}"></h:outputText>
			</h:column>
		</richfaces:suggestionbox>

</ui:composition>

...
    public List<Operador> autocomplete(Object suggest) throws DaoException {
        String pref = (String)suggest;
        ArrayList<Operador> result = new ArrayList<Operador>();

        Iterator<Operador> iterator = ((ArrayList<Operador>)todosOperadores()).iterator(); 
        while (iterator.hasNext()) {
            Operador elem = ((Operador) iterator.next());
            if ((elem.getNome() != null && elem.getNome().toLowerCase().indexOf(pref.toLowerCase()) == 0) || "".equals(pref)){
                result.add(elem);
            }
        }
        return result;
    }
...