fix(model): throw readable error when calling Model() with a string instead of model()

lib/model.js

@@ -13,6 +13,7 @@ const EventEmitter = require('events').EventEmitter;
 const Kareem = require('kareem');
 const MongooseBuffer = require('./types/buffer');
 const MongooseError = require('./error/index');
+const ObjectParameterError = require('./error/objectParameter');
 const OverwriteModelError = require('./error/overwriteModel');
 const Query = require('./query');
 const SaveOptions = require('./options/saveOptions');
@@ -118,10 +119,15 @@ const saveToObjectOptions = Object.assign({}, internalToObjectOptions, {
 
 function Model(doc, fields, skipId) {
   if (fields instanceof Schema) {
-    throw new TypeError('2nd argument to `Model` must be a POJO or string, ' +
+    throw new TypeError('2nd argument to `Model` constructor must be a POJO or string, ' +
       '**not** a schema. Make sure you\'re calling `mongoose.model()`, not ' +
       '`mongoose.Model()`.');
   }
+  if (typeof doc === 'string') {
+    throw new TypeError('First argument to `Model` constructor must be an object, ' +
+      '**not** a string. Make sure you\'re calling `mongoose.model()`, not ' +
+      '`mongoose.Model()`.');
+  }
   Document.call(this, doc, fields, skipId);
 }
 
@@ -3099,6 +3105,9 @@ Model.$__insertMany = function(arr, options, callback) {
   const toExecute = arr.map((doc, index) =>
     callback => {
       if (!(doc instanceof _this)) {
+        if (doc != null && typeof doc !== 'object') {
+          return callback(new ObjectParameterError(doc, 'arr.' + index, 'insertMany'));
+        }
         try {
           doc = new _this(doc);
         } catch (err) {

test/model.test.js

@@ -7295,6 +7295,13 @@ describe('Model', function() {
     const isCapped = await TestModel.collection.isCapped();
     assert.ok(isCapped);
   });
+
+  it('throws helpful error when calling Model() with string instead of model() (gh-14281)', async function() {
+    assert.throws(
+      () => mongoose.Model('taco'),
+      /First argument to `Model` constructor must be an object/
+    );
+  });
 });