Comment 2 for bug 1499391

I've tried to upgrade from 16.10 to 17.04 and got the same error.

Changed /usr/sbin/do-release-upgrade from

    print(_("For upgrade information, please visit:\n"
            "%(url)s\n") % { 'url' : url })

to

    print(_("For upgrade information, please visit:\n %(url)s\n") % { 'url' : url })

and upgrade have started.

Ubuntu - ignoring bugs over centuries! ))