I don't see how this person could have gotten a string instead
of
vector due to this advice, because viper-read-key-sequence always
returns an object that was returned by the regular
read-key-sequence.
In viper-3.11.1 of September 9, 2001 the advice puts value returned by
`viper-events-to-keys' to `keys'. `viper-events-to-keys' may return
string.