My second PL/pgSQL function - minor problem

Hey all,

http://pastebin.com/f1015226d

The above function appears to be doing exactly what I want: Fetch the users
data and update the visits column, if the supplied credentials match a user.

My problem is what happens when the credentials don't match a user. In those
cases I would like to have a boolean false returned, but instead I get an
empty array - which of course is entirely according to the functions "RETURN
SETOF users" statement.

Is this little problem solvable, or will I have to learn to live with the
empty array?

Regards,
Thomas