validation issue in custom field and custom shortcode

Hello there I was able to implement a custom shortcode and field in CF7 in order to get a list of the last 24 month of the year in italian language on a select input box.

Non my last point is how to validate the field in case empty and not selected???

Please help

Here is my script:

<?php

/* get months in php */

 function mesi_anno2() {
 $mese = array ("Gennaio-", "Febbraio-", "Marzo-", "Aprile-", "Maggio-", "Giugno-", "Luglio-", "Agosto-", "Settembre-", "Ottobre-", "Novembre-", "Dicembre-");
 $str="";
        for($i = 0; $i < 24; $i++) {
        $time = mktime(0, 0, 0, date('n') - $i);
        $str .="<option value=".$mese[(date("n", $time)-1)].date("Y", $time).">".$mese[(date("n", $time)-1)].date("Y", $time)."</option>";
    }
  return $str;
   } 

/* shortcode */

wpcf7_add_shortcode('custom_date',  'wpcf7_custom_date_shortcode_handler', true);
wpcf7_add_shortcode('custom_date*', 'wpcf7_custom_date_shortcode_handler', true);

function wpcf7_custom_date_shortcode_handler($tag) {

    if (!is_array($tag)) return '';

    $name = $tag['name'];
    if (empty($name)) return '';

	$validation_error = wpcf7_get_validation_error( $tag->name );

	$class = wpcf7_form_controls_class( $tag->type );

	if ( $validation_error )
		$class .= ' wpcf7-not-valid';

      $html = '
	  <select name="'.$name.'">
 	  <option value="">---</option>
 	  '.mesi_anno2().'
 	  </select>';

return $html;
}

add_filter('wpcf7_custom_date',  'custom_date_filter', 10, 2);
add_filter('wpcf7_custom_date*', 'custom_date_filter', 10, 2);  

function wpcf7_custom_date_validation_filter( $result, $tag ) {
	$tag = new WPCF7_Shortcode( $tag );

	$name = $tag->name;

	if ( isset( $_POST[$name] ) && is_array( $_POST[$name] ) ) {
		foreach ( $_POST[$name] as $key => $value ) {
			if ( '' === $value )
				unset( $_POST[$name][$key] );
		}
	}

	if ( $tag->is_required() ) {
		if ( ! isset( $_POST[$name] )
		|| empty( $_POST[$name] ) && '0' !== $_POST[$name] ) {
			$result['valid'] = false;
			$result['reason'][$name] = 'ERRORE';
		}
	}

	return $result;
}

?>

http://wordpress.org/plugins/contact-form-7/