PHP-Notice on author.php when no posts

Hello my friends,

i am using that theme: http://press75.com/view/debut/
WB_DEBUG is true.

There was no author.php so I made one. it works without problems, but I get a PHP-Notice-Error, wenn I visit an author page from an author, who is registered but doesnt release a post yet:

Notice: Trying to get property of non-object in C:\xampp\htdocs\wp\wp-includes\post-template.php on line 30

On line 30 is following code, which is called somewhere in wp_head (dont know where in detail):

function get_the_ID() {
	global $post;
	return $post->ID;
}

do u know what can i do to remove that error?

thanks a lot!

alex