What does this code do?

[Kai Großjohann]

There's this piece of code in tramp.el; does anyone know what it does?

(defun tramp-parse-passwd (filename)
  "Return a list of (user host) tuples allowed to access.
Host is always \"localhost\"."

  (let (res)
    (if (and (symbolp 'user) (zerop (length user)))
        '(("root" nil))

Why does it refer to the symbol user?
-- 
A turnip curses Elvis