spring @Valid annotation not working

When i added @Valid annotation at that time post method doesn't call and without @Valid annotation, post method is call. I don't know why this happen? my code is below.

Bean.java

public class Bean {

    @NotEmpty(message="firstname is required.")
    private String firstname;

    @NotEmpty(message="lastname is required.")
    private String lastname;

    //getter and setter method
}

Controller.java

    @RequestMapping(value="/add", method=RequestMethod.POST)
    public String addForm(ModelMap model, @Valid @ModelAttribute(value="bean") Bean bean, 
            BindingResult result) {

        if(result.hasErrors())
            return "registration";

        return "registration";
    }

registration.jsp

<div>
    <c:url value="/merchant/handleRegistration" var="registrationURL"></c:url>
    <form:form action="${registrationURL}" id="registrationForm" method="POST" modelAttribute="bean">
    <form:errors path="*"  element="div" />
        <table>
            <tr>
                <td><form:label path="firstname">Firstname* : </form:label></td>
                <td><form:input path="firstname" cssClass="required" /></td>
                <td><form:errors path="firstname" cssClass="error" /></td>
            </tr>
            <tr>
                <td><form:label path="lastname">Lastname* : </form:label></td>
                <td><form:input path="lastname" cssClass="required" /></td>
                <td><form:errors path="lastname" cssClass="error" /></td>
            </tr>
            <tr>
                <td colspan="3"><input type="submit" value="Register" ></td>
            </tr>
        </table>
    </form:form>