public String update() {
        getDao().update(getInstance());
        return SUCCESS;
}

    public Account getInstance() {

        //setId(new Long("1"));

        if (instance == null) {
            if (id != null) {
                instance = loadInstance();
            } else {
                instance = createInstance();
            }
        }

        return instance;
    }

<f:metadata>
    <f:viewParam name="accountId" value="#{accountMB.id}" />
</f:metadata>

<h:form prependId="false">

    <h:inputHidden id="id" value="#{accountMB.instance.id}"/>

    <h:inputText id="firstName" value="#{accountMB.instance.firstName}"/>

    <h:commandButton type="submit" action="#{accountMB.update}" value="Сохранить" />

</h:form>

java.sql.SQLException: ORA-01407: cannot update ("MYBD"."ACCOUNTS"."EMAIL") to NULL