ypeError：无法在db.collection.findOne上将undefined或null转换为对象（错误的性质已更改）

Question

正如标题所示，在我的一个后端路由中使用findOne函数时出现以下错误：

/home/liam/Documents/aiRegister/node_modules/mongodb/lib/utils.js:123
process.nextTick(function() { throw err; });
                              ^

TypeError: Cannot convert undefined or null to object
at db.collection.findOne (/home/liam/Documents/aiRegister/app/routes

/user_routes.js:14:16)
    at handleCallback (/home/liam/Documents/aiRegister/node_modules/mongodb/lib/utils.js:120:56)
    at /home/liam/Documents/aiRegister/node_modules/mongodb/lib/collection.js:1416:5
    at handleCallback (/home/liam/Documents/aiRegister/node_modules/mongodb/lib/utils.js:120:56)
    at /home/liam/Documents/aiRegister/node_modules/mongodb/lib/cursor.js:683:5
    at handleCallback (/home/liam/Documents/aiRegister/node_modules/mongodb-core/lib/cursor.js:171:5)
    at setCursorNotified (/home/liam/Documents/aiRegister/node_modules/mongodb-core/lib/cursor.js:515:3)
    at /home/liam/Documents/aiRegister/node_modules/mongodb-core/lib/cursor.js:599:16
    at queryCallback (/home/liam/Documents/aiRegister/node_modules/mongodb-core/lib/cursor.js:232:18)
    at /home/liam/Documents/aiRegister/node_modules/mongodb-core/lib/connection/pool.js:469:18

这是我的代码：

   //Get user
  app.get('/user/:token', (req, res) => {
    const details = {
      'token': req.params.token
    };
    db.collection('users').findOne(details, (err, item) => {
      if (err) {
        res.send({
          'error': 'An error has occurred'
        });
      } else {
        delete item.token;
        res.send(item);
      }
    });
  });

我更新了npm和node以及所有已安装的软件包，没有运气。提前谢谢。

编辑：似乎错误来自＆＃39;删除item.token;＆＃39;因为事实证明，该文件不存在。然而，这引发了一个问题，即为什么文档不存在，即使它被添加（或者我认为。事实证明，添加用户的路径没有运行，但是我的前端正在返回成功。这是代码：

//Add user
  app.post('/user', (req, res) => {
    const user = {
      email: req.body.email,
      name: req.body.name,
      token: req.body.token
    };
    const details = {
      email: req.body.email
    };
    console.log("Adding user...");
    db.collection('users').remove(details, (err, item) => {
      if (err) {
        res.send({
          'error': 'An error has occurred'
        });
      } else {
        console.log("User del...");
      }
    });
    db.collection('users').insert(user, (err, result) => {
      if (err) {
        res.send({
          'error': 'An error has occurred'
        });
      } else {
        res.send(result.ops[0]);
        console.log("User added");
      }
    });
  });

在我的前端：

$.ajax({
      type: "post",
      url: "/api/user",
      data: {
        name: user["displayName"],
        email: user["email"],
        token: token
      },
      success: console.log("Success!")
    });

我不知道为什么会这样。