Fix issues #6356 on master (#7170)

* fix ER_EMPTY_QUERY error on update with virtual fields for master

* fix review

* [ci skip] Changelog for #6356

changelog.md

 # Future
+- [FIXED] Updating `VIRTUAL` field throw `ER_EMPTY_QUERY` [#6356](https://github.com/sequelize/sequelize/issues/6356)
 - [FIXED] Fix `Instance.decrement` precision problems [#7112](https://github.com/sequelize/sequelize/pull/7112)
 - [FIXED] MSSQL tedious debug regression fix when dialectOptions are not passed [#7130](https://github.com/sequelize/sequelize/pull/7130)
 - [CHANGED] `setIsolationLevelQuery` to skip under MSSQL dialect, added debug listener for tedious [#7130](https://github.com/sequelize/sequelize/pull/7130)

lib/model.js

@@ -3451,7 +3451,8 @@ class Model {
         return instance.save(includeOptions).then(() => this[include.association.accessors.set](instance, {save: false, logging: options.logging}));
       });
     }).then(() => {
-      if (!options.fields.length) return this;
+      const realFields = options.fields.filter((field) => !this.constructor._isVirtualAttribute(field));
+      if (!realFields.length) return this;
       if (!this.changed() && !this.isNewRecord) return this;
 
       const versionFieldName = _.get(this.constructor.rawAttributes[versionAttr], 'field') || versionAttr;

test/integration/instance.test.js

@@ -1213,6 +1213,21 @@ describe(Support.getTestDialectTeaser('Instance'), function() {
           });
         });
       });
+
+      it('should not throw ER_EMPTY_QUERY if changed only virtual fields', function() {
+        const User = this.sequelize.define('User' + config.rand(), {
+          name: DataTypes.STRING,
+          bio: {
+            type: DataTypes.VIRTUAL,
+            get: () => 'swag'
+          }
+        }, {
+          timestamps: false
+        });
+        return User.sync({force: true}).then(() => (
+          User.create({ name: 'John', bio: 'swag 1' }).then((user) => user.update({ bio: 'swag 2' }).should.be.fulfilled)
+        ));
+      });
     });
 
     it('updates with function and column value', function() {