[rt-users] Upgrade 3.6.5->3.8.7: Duplicate entry '' for key 2

[Howard Jones]

I've been doing a test migration from RT 3.6.5 to 3.8.7 on a spare VM, 
prior to doing it on our live server. I noticed there were a lot of db 
changes, and wanted to be sure that it would all be smooth, and that I 
knew how long it would be down. Good thing I did, because while running 
the schema update script produced by upgrade-mysql-schema.pl, I get:

ERROR 1062 (23000): Duplicate entry '' for key 2

After breaking all the ALTER statements into single changes, the 
offending one is the very last one:
   ALTER TABLE Users MODIFY Name VARCHAR(200) CHARACTER SET utf8 NOT 
NULL DEFAULT '';

I have only one user with a name of ''. I have changed that to 
'randomstring', and I still get this error. As I understand it, it's to 
do with how mysql transliterates from one character set to another. So 
how can I figure out which of my 35000 usernames will transliterate to 
an empty string? No doubt the users in question are spammers, but I 
still need to find them to fix them...

Also, am I right to assume that it's OK to just change the Name field? 
It's the ID that is used elsewhere, right?

Thanks,

Howie