为什么在collection.replaceOne之后，我的res.statusCode从200变成了404？

const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:27017';
const dbName = 'mydb';

MongoClient.connect(url, function(err, client) {
  if (err) {
    console.error('Failed to connect to MongoDB:', err);
    return;
  }

  const db = client.db(dbName);
  const collection = db.collection('mycollection');

  const filter = { name: 'John' };
  const replacement = { name: 'Jane', age: 30 };

  collection.replaceOne(filter, replacement, function(err, result) {
    if (err) {
      console.error('Failed to replace document:', err);
      return;
    }

    if (result.matchedCount === 0) {
      console.log('No document found for replacement');
      return;
    }

    console.log('Document replaced successfully');
  });
});