Various comment functions reporting error when `get_comment()` returns `null`

[thomasplevy]

While working on #53290 I noticed that if the function get_comment_author_link() is called with no value passed into it or if an invalid comment ID is passed into the function an error is thrown on the return filter:

Trying to get property 'comment_ID' of non-object
wp-includes/comment-template.php:242

While gathering information to report this I also noticed several other functions in the same file, wp-includes/comment-template.php will suffer from the same or a similar issue:

+ comment_author()
+ get_comment_author_email()
+ comment_author_email()
+ get_comment_author_IP()
+ comment_author_url()
+ get_comment_excerpt()
+ comment_excerpt()
+ get_comment_type()

Some of the functions in this file, get_comment_author() for example, store the comment ID as a variable and pass that into the return filter:

$comment_ID = ! empty( $comment->comment_ID ) ? $comment->comment_ID : $comment_ID;

I'm currently working on writing tests since most of the functions I'm mentioned don't have existing test coverage.

I'm also uploading a patch with my proposed solution. If this seems like the right direction to go I'll add changes to the remaining functions and update the patch (and tests).

[SergeyBiryukov]

Hi there, welcome back to WordPress Trac! Thanks for the ticket.

Just linking to some related tickets here: #40143, #54149.

Trac ticket: https://core.trac.wordpress.org/ticket/57615

Updated the functions I mentioned in the trac ticket and wrote / updated unit tests for related code.

I swore that I read a while back the the null coalesce operator was now allowed by the WP coding standards now but in rereading I was incorrect, it said the null coalesce *will be allowed* when the PHP minimum is raised to 7.0. I'll update shortly.

[hellofromTonya]

Removing trunk as the Version as the issue does not appear to be introduced in the 6.2.0 cycle.