Undefined index notice when signing up for username in multisite

[jfarthing84]

The following notice is displayed when signing up for a multisite username only:

Notice: Undefined index: add_to_blog in D:\www\wordpress-3.1-multisite\wp-includes\ms-functions.php on line 1863

This is because there is no isset() check on the $meta array for the key of 'add_to_blog'.

[kawauso]

Being pedantic: !empty()

[boonebgorges]

Bump. I was just about to submit this very patch.

[nacin]

empty looks correct over isset, as a blog ID of 0 is invalid.

[ryan]

In [17794]:

Check if empty to avoid noticed when signing up for username in multisite. Props jfarthing84, kawauso. fixes #16680