unique keys and indexes must be NOT NULL or MySQL fucks up

unique keys and indexes must be NOT NULL or MySQL fucks up

If this merge throws exception on scripts/upgrade.php and you recently
tried a nightly (i.e. during 2015-02-19) then just go back a commit or two
and try again.

Or delete the duplicate entries. Find the entries like this:

SELECT COUNT(*), urlhash FROM file_redirection
    GROUP BY urlhash
    HAVING COUNT(*) > 1;

then for each urlhash (or come up with a smart SQL query) do:
DELETE FROM file_redirection WHERE urlhash='hashfrompreviousquery' LIMIT 1;

You'll have to remove duplicates more than once if you have >2 identical
urlhash entries. LIMIT -1 might do that for you. I'm not sure.