Description:
------------
Per http://bugs.php.net/bug.php?id=40797, the behavior of empty() was modified to call the __isset magic method.  There is at least one case where this changes the behavior of empty() to falsely report "not empty" when in fact the desired result is "empty".

I suppose you would need an __empty() magic method, but that sounds heinous.  Overloading docs should at least be updated to warn the developer.

Reproduce code:
---------------
<?
class myclass
{
    private $_raw_data = array() ;

    function __construct( $data)
    {
        $this->_raw_data = $data ;
    }

    function __isset( $field_name)
    {
        return isset($this->_raw_data[$field_name]);
    }    
}

$_POST['foo']='' ;
$myclass = new myclass( $_POST) ;

// correct reports "isset"
echo (isset($myclass->foo)) ? 'isset' : 'not isset') ;

// incorrectly reports "not empty"
echo (empty($myclass->foo)) ? 'empty' : 'not empty' ;

// a way to get around the broken empty() call
echo ($myclass->foo) ? 'not empty' : 'empty' ;

?>

Expected result:
----------------
isset
empty
empty

Actual result:
--------------
isset
not empty
empty