code: public Object getGetterOrSetter(String name, int index, boolean isSetter)
      {
          if (name != null && index != 0)
              throw new IllegalArgumentException(name);
          Slot slot = slotMap.query(name, index);
          if (slot == null)
              return null;
          if (slot instanceof GetterSlot) {
              GetterSlot gslot = (GetterSlot)slot;
              Object result = isSetter ? gslot.setter : gslot.getter;
              return result != null ? result : Undefined.instance;
          }
          return Undefined.instance;
      }
docs: Get the getter or setter for a given property. Used by __lookupGetter__
  and __lookupSetter__.
  
  @param name Name of the object. If nonnull, index must be 0.
  @param index Index of the object. If nonzero, name must be null.
  @param isSetter If true, return the setter, otherwise return the getter.
  @exception IllegalArgumentException if both name and index are nonnull
  and nonzero respectively.
  @return Null if the property does not exist. Otherwise returns either
  the getter or the setter for the property, depending on
  the value of isSetter (may be undefined if unset).