- (aver class)
- (aver (typep class 'built-in-class)))
- `(type ,specializer ,parameter))
+ ;; CLASS can be null here if the user has erroneously
+ ;; tried to use a defined type as a specializer; it
+ ;; can be a non-BUILT-IN-CLASS if the user defines a
+ ;; type and calls (SETF FIND-CLASS) in a consistent
+ ;; way.
+ (when (and class (typep class 'built-in-class))
+ `(type ,specializer ,parameter))))