code: func (l *waiterList) PushBackList(m *waiterList) {
  	if l.head == nil {
  		l.head = m.head
  		l.tail = m.tail
  	} else if m.head != nil {
  		waiterElementMapper{}.linkerFor(l.tail).SetNext(m.head)
  		waiterElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
  
  		l.tail = m.tail
  	}
  
  	m.head = nil
  	m.tail = nil
  }
docs: // PushBackList inserts list m at the end of list l, emptying m.