anchor.diff:    (declare (type cons hint-and-bulk))
     (destructuring-bind (hint . bulk) hint-and-bulk
       (declare (type fixnum hint)
  -             (type bulk-task bulk))
  +             (type (or null bulk-task) bulk))
  +    (when (null bulk)
  +      (return-from bulk-find-task))
       (let* ((subtasks (bulk-task-subtasks bulk))
              (begin    hint)
              (end      (length subtasks)))
         (loop
           (when (zerop (bulk-task-waiting bulk))
  +          (setf (cdr hint-and-bulk) nil)
             (return (values nil nil)))
           (let ((index (position nil subtasks :start begin :end end :test-not #'eql)))
             (cond (index
  
positive.code:            "EXECUTE-TASK"
             "STACK" "MAKE" "P"
             "PUSH" "PUSH-ALL" "STEAL" "RUN-ONE"))
  
  (in-package "WORK-STACK")
  
  
negative.code:   (etypecase task
      ((or symbol function)
       (funcall task))
      (task
       (funcall (task-fun task) task))))
  
  