java.lang.IllegalArgumentException: attempt to create event with null entity - spring

Question

I trying persist this entity:
#Entity
public class Cliente extends Model {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;
#OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Usuario usuario;
#OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private org.loja.model.cesta.Cesta cesta;
#OneToMany(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
#OrderColumn
private List<org.loja.model.pedido.Pedido> pedidos;
public Cliente() {
this.usuario = new Usuario();
this.cesta = null;
this.pedidos = null;
}
}
with this form:
<form class="form-signin" id="form" method="post" th:action="#{/register}">
<label for="username" class="sr-only">Username</label>
<input type="text" name="usuario.username" id="username" class="form-control" placeholder="Username" required autofocus>
<label for="password" class="sr-only">Password</label>
<input type="password" name="usuario.password" id="password" class="form-control" placeholder="Password" required>
<label for="firstName" class="sr-only">Nome</label>
<input type="text" name="usuario.firstName" id="firstName" class="form-control" placeholder="Nome" required>
<label for="lastName" class="sr-only">Sobrenome</label>
<input type="text" name="usuario.lastName" id="lastName" class="form-control" placeholder="Sobrenome" required>
<label for="email" class="sr-only">E-mail</label>
<input type="email" name="usuario.email" id="email" class="form-control" placeholder="E-mail" required>
</form>
I also tried this:
<form class="form-signin" id="form" method="post" th:object="${command}" th:action="#{/register}">
<label for="username" class="sr-only">Username</label>
<input type="text" th:field="*{usuario.username}" id="username" class="form-control" placeholder="Username" required autofocus>
<label for="password" class="sr-only">Password</label>
<input type="password" th:field="*{usuario.password}" id="password" class="form-control" placeholder="Password" required>
<label for="firstName" class="sr-only">Nome</label>
<input type="text" th:field="*{usuario.firstName}" id="firstName" class="form-control" placeholder="Nome" required>
<label for="lastName" class="sr-only">Sobrenome</label>
<input type="text" th:field="*{usuario.lastName}" id="lastName" class="form-control" placeholder="Sobrenome" required>
<label for="email" class="sr-only">E-mail</label>
<input type="email" th:field="*{usuario.email}" id="email" class="form-control" placeholder="E-mail" required>
</form>
But I keep getting the error:
java.lang.IllegalArgumentException: attempt to create event with null entity
when I try submit the data.
my controller:
#RequestMapping(value = "/register", method=RequestMethod.GET)
public String formRegister(Model model) {
model.addAttribute("command", new Cliente());
return "register";
}
#RequestMapping(value = "/register", method=RequestMethod.POST)
#ResponseBody
public void doRegister(#ModelAttribute("cliente") Cliente object) throws Exception {
home.register(object);
}
Anyone can give a hint of what's wrong here?