bug:the “post_link” filter using function can not use the get_permalink()

this is my code:

/*
Plugin Name: TEST MYPERMALINK
Plugin URI: http://www.pkphp.com/
Description: Create every post to HTML cahe file, and refresh automatic.
Version: 1.0
Author: Askie
Author URI: http://www.pkphp.com/
*/

function Mypermalink($post_url,$post)
{
	if (false)
	{
		return "my permalink";
	}
	else
	{
		return get_permalink($post->ID);
	}
}

add_filter('post_link',"Mypermalink",1,2);

active the code ,the wordpress will return a blank screen !

what i want is to write a real html cache plugin , and the bug is display when i try to change the default post permalink!

someone want to test this code please save the code as a plugin file in you wp plugins folder and active the code ,then you visit your wp home page, the bug will display!