[racket] curious behavior of path-replace-suffix for files beginning with dot?

Looking over the
documentation<http://docs.racket-lang.org/reference/Manipulating_Paths.html#(def._((lib._racket/private/misc..rkt)._path-replace-suffix))>
I'm
not clear why this would be so:

> (path-replace-suffix (string->path ".foobar") "")

#<path:?>


If the behavior is undefined, seems like path-replace-suffix ought to raise
an error rather than return a path that is a single question mark. Or am I
missing something?
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