getgpc($k, $t='GP')，怎么返回的是 NULL?

<?php
/**
 * 实用小代码
 * 获得GET POST COOKIS
 */
$html=<<<WORD
<form method="post">
    <p>First name: <input type="text" name="fname" /></p>
    <p>Last name: <input type="text" name="lname" /></p>
    <input type="submit" value="Submit" />
</form>
WORD;
ECHO $html;
//var_dump($_GET);
var_dump($_POST);

function getgpc($k, $t='GP') {
    $t = strtoupper($t);
    switch($t) {
        case 'GP' : isset($_POST[$k]) ? $var = &$_POST : $var = &$_GET; break;
        case 'G': $var = &$_GET; break;
        case 'P': $var = &$_POST; break;
        case 'C': $var = &$_COOKIE; break;
        case 'R': $var = &$_REQUEST; break;
    }
    return $var[$k];
    return isset($var[$k]) ? $var[$k] : null;
}

$view_off = getgpc('view_off');
var_dump($view_off);

求解，万能的PHP圈友为什么返回的是NULL 值 。