fix(mongoose): handle initially null driver when instantiating Mongoo…

…se for rollup

Fix #12335

lib/index.js

@@ -4,10 +4,14 @@
  * Module dependencies.
  */
 
-require('./driver').set(require('./drivers/node-mongodb-native'));
+const mongodbDriver = require('./drivers/node-mongodb-native');
+
+require('./driver').set(mongodbDriver);
 
 const mongoose = require('./mongoose');
 
+mongoose.setDriver(mongodbDriver);
+
 mongoose.Mongoose.prototype.mongo = require('mongodb');
 
 module.exports = mongoose;

lib/mongoose.js

@@ -68,8 +68,8 @@ function Mongoose(options) {
     autoCreate: true,
     autoSearchIndex: false
   }, options);
-  const createInitialConnection = utils.getOption('createInitialConnection', this.options);
-  if (createInitialConnection == null || createInitialConnection) {
+  const createInitialConnection = utils.getOption('createInitialConnection', this.options) ?? true;
+  if (createInitialConnection && this.__driver != null) {
     const conn = this.createConnection(); // default connection
     conn.models = this.models;
   }
@@ -169,6 +169,9 @@ Mongoose.prototype.setDriver = function setDriver(driver) {
   const oldDefaultConnection = _mongoose.connections[0];
   _mongoose.connections = [new Connection(_mongoose)];
   _mongoose.connections[0].models = _mongoose.models;
+  if (oldDefaultConnection == null) {
+    return _mongoose;
+  }
 
   // Update all models that pointed to the old default connection to
   // the new default connection, including collections