fix(model): return deep cloned value for toJSON (#10058)

lib/model.js

@@ -4201,7 +4201,7 @@ class Model {
    * @returns {Object}
    */
   toJSON() {
-    return _.clone(
+    return _.cloneDeep(
       this.get({
         plain: true
       })

test/unit/instance/to-json.test.js

@@ -22,5 +22,24 @@ describe(Support.getTestDialectTeaser('Instance'), () => {
       const json2 = user.toJSON();
       expect(json2).to.have.property('name').and.be.equal('my-name');
     });
+
+    it('returns clone of JSON data-types', () => {
+      const User = current.define('User', {
+        name: DataTypes.STRING,
+        permissions: DataTypes.JSON
+      });
+      const user = User.build({ name: 'my-name', permissions: { admin: true, special: 'foobar' } });
+      const json = user.toJSON();
+
+      expect(json)
+        .to.have.property('permissions')
+        .that.does.not.equal(user.permissions);
+
+      json.permissions.admin = false;
+
+      expect(user.permissions)
+        .to.have.property('admin')
+        .that.equals(true);
+    });
   });
 });