我對(duì) head.next 如何返回整個(gè)列表而不是下一個(gè)值感到困惑，例如下面的代碼中的 l1,l2,dummy .next。特別是我想知道 head.next 如何返回整個(gè)排序數(shù)組并跳過在第二行輸入的 -1 值。let mergeTwoLists = function (l1, l2) {  let dummy = new ListNode(-1);  let head = dummy;  while (l1 !== null && l2 !== null) {    if (l1.val <= l2.val) {      dummy.next = l1;      l1 = l1.next;    } else {      dummy.next = l2;      l2 = l2.next;    }    dummy = dummy.next;  }  if (l1 !== null) {    dummy.next = l1;  } else {    dummy.next = l2;  }  return head.next;};class ListNode {  constructor(val = null, next = null) {    this.val = val;    this.next = next;  }}