unbound-slot,
cell-error,
error,
serious-condition,
condition,
t
The object having the unbound slot is initialized by
the :instance initialization argument to make-condition,
and is accessed by the function unbound-slot-instance.
The name of the cell (see cell-error) is the name of the slot.
cell-error-name, unbound-slot-instance, Section 9.1 (Condition System Concepts)