Comment 2 for bug 1311421

On second thought, I suppose this violates the specification (http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/sec_22-1-3-4.html), which says that a double-quote must be printed before and after. Therefore "" would be the representation of an empty string with characters of type nil.

Thus the fix would be to signal an error when an element of an empty-type string is accessed via the stream functionality, just as using AREF signals an error.