PHP debug notices when deleting a WordPress user

[henry.wright]

Steps to reproduce:

1. Disable BuddyPress
2. Create a new user by going to Users > Add New in the admin area
3. Enable BuddyPress
4. Go to Users > All Users in the admin area
5. Tick the checkbox next to the user you just created.
6. Select Delete from the "Bulk Actions" option list and click on the Apply button.

[DJPaul]

@henry.wright It'd be useful if you could copy/paste the debug notice for reports like this, please. :)

[henry.wright]

@DJPaul I just tried to grab a screenshot for you but I can't seem to reproduce this problem now. I will close and reopen if it happens again.

[henry.wright]

So I experienced this issue again and this time I managed to grab a screenshot. See the attached file.

[DJPaul]

Odd - something to do with our wpdb->delete call, maybe it's not in the right format.

[djpaul]

In 10748:

Activity: add test for deleting user when they have no bp_last_activity cache set.

See #6981

[DJPaul]

If you create a new user as described then immediately delete it, it never has a last_activity set. BP_Core_User::delete_last_activity() assumes it always will, and a null value gets passed to wpdb->delete which chokes wpdb->prepare which throws the "doing_it_wrong" error.

I've added a test in r10748 to capture this.

[djpaul]

In 10749:

Core: when deleting a user's last_activity value, make sure it exists.

Creating a user in wp-admin then immediately deleting it was causing a
"doing it wrong" error because the last_activity value was null,
causing WPDB's delete and prepare methods to fail.

Fixes #6981