file-readable-p returns t for empty string

[Järneström Jonas]

In GNU Emacs 20.6.1 (sparc-sun-solaris2.6, X toolkit)
 of Fri Mar  3 2000 on iris
configured using `configure  --with-gcc --with-pop --with-x-toolkit=lucid 
--bindir=/usr/local/bin --libexecdir=/usr/local/libexec'

(file-readable-p "") returns t.
Wouldnt nil be more appropriate since there is no filename to visit
(or whatever) despite the returning t?
Same behavior for its peers like file-exists-p an so on...