code: func (list *LinkedList) RemoveBack() (interface{}, bool) {
  	list.key.Lock()
  	defer list.key.Unlock()
  
  	if list.last == nil {
  		return nil, false
  	}
  
  	retval := list.last.payload
  	list.length--
  
  	if list.length == 0 {
  		list.first = nil
  	} else {
  		node, _ := get(list.first, list.length-1)
  		node.next = nil
  	}
  	return retval, true
  }
docs: // RemoveBack returns the entry logically stored at the back of this list and removes it.