Guile happily compiles the following module:
(define-module (test))
(define (foo) #t)
(export (foo))
This exports foo as (), because (foo) = (foo . ()) and export treats pairs as renaming.
If you use this module, readline breaks because it looks up the module's exported symbols and then tries to call (symbol->string '()):
scheme@(guile-user)> (use-modules (test))
scheme@(guile-user)> x<TAB>
While reading _expression_:
ERROR: In procedure symbol->string: Wrong type argument in position 1 (expecting symbol): ()