fix(addScope): only throw when defaultScope is defined (#9703)

lib/model.js

@@ -1423,7 +1423,7 @@ class Model {
       override: false
     }, options);
 
-    if ((name === 'defaultScope' || name in this.options.scopes) && options.override === false) {
+    if ((name === 'defaultScope' && Object.keys(this.options.defaultScope).length > 0 || name in this.options.scopes) && options.override === false) {
       throw new Error('The scope ' + name + ' already exists. Pass { override: true } as options to silence this error');
     }
 

test/unit/model/scope.test.js

@@ -294,6 +294,14 @@ describe(Support.getTestDialectTeaser('Model'), () => {
       }).to.throw('The scope defaultScope already exists. Pass { override: true } as options to silence this error');
     });
 
+    it('should not warn if default scope is not defined', () => {
+      const Model = current.define('model');
+    
+      expect(() => {
+        Model.addScope('defaultScope', {});
+      }).not.to.throw();
+    });
+
     it('allows me to override a default scope', () => {
       Company.addScope('defaultScope', {
         include: [Project]