Notice thrown in get_page_template_slug in certain conditions

[tollmanz]

When get_page_template_slug() is called outside of the loop and get_post returns null, the check of $post->post_type will trigger the notice:

Notice: Trying to get property of non-object in /path/to/root/wp-includes/post-template.php on line 1284

Steps to reproduce:

1. Remove all posts from site (or just trash them)
2. Add the test code below to Twenty Thirteen's functions.php (making sure that Twenty Thirteen is activated)
3. Load the front page
4. Notice will appear

function test_get_page_template_slug() {
	get_page_template_slug();
}
add_action( 'init', 'test_get_page_template_slug' );

I'm marking as 3.4 since get_page_template_slug() was introduced then.

[tollmanz]

The diff file also improves the $post_id PHPDoc as it can be null as well as an int.

[SergeyBiryukov]

In 24191:

Avoid a PHP notice in get_page_template_slug() if the page does not exist. props tollmanz. fixes #24250.

[SergeyBiryukov]

#23340 was marked as a duplicate.