T4: Problem with my own Date Validator

[César Augusto Mateus]

Hi all,
I did a Validator with the purpose of not to allow that a user entered a
date before of today.
That validation work fine, but not yet i can to do that this validator is
obligatory, because when i enter a null value, the validator was not call.
My Validator code here, thanks

package co.org.amv.rupm.tapestry.models;

import java.util.Date;

import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;
import org.apache.tapestry.form.FormComponentContributorContext;
import org.apache.tapestry.form.IFormComponent;
import org.apache.tapestry.form.ValidationMessages;
import org.apache.tapestry.form.validator.BaseValidator;
import org.apache.tapestry.form.validator.Validator;
import org.apache.tapestry.valid.ValidationConstants;
import org.apache.tapestry.valid.ValidatorException;

public class ValidatorFecAntesHoyRequired extends BaseValidator implements
Validator  {


    public void validate(
            IFormComponent field, ValidationMessages messages, Object
object)
    throws ValidatorException {
        Date fecha = (Date) object;
//   IF THE USER ENTER A NULL VALUE, NEVER PAINT THIS
        System.out.println("----"+fecha);
//  THEN NEVER THROW THIS EXCEPTION
        if( fecha == null ){
            throw new ValidatorException( field.getDisplayName() + ": Debe
ingresar un valor", null );
        }
        Date hoy = new Date();
        if( fecha.after( hoy ) ){
            throw new ValidatorException(
                    field.getDisplayName() + ": La fecha no puede ser
posterior a la fecha actual", null );
        }
    }

    public boolean getAcceptsNull() {
        return false;
    }

    public boolean isRequired() {
        return true;
    }

    public void renderContribution(
            IMarkupWriter arg0, IRequestCycle cycle,
            FormComponentContributorContext context, IFormComponent field) {
    }

}

Thanks for your help, Which is my error???