`bulkCreate`'s `updateOnDuplicate` option default does not work

What are you doing?

I am creating entities in bulk with bulkCreate. In case of a conflict on the primary key, I want that entity to be updated with the new values I have given.

await Asset.destroy({ where: {} });

await Asset.create({
    id: 1,
    uuid: 'uuid-1',
    name: 'asset-1',
});

await Asset.bulkCreate([
    {
        id: 2,
        uuid: 'uuid-2',
        name: 'asset-2',
    },
    {
        id: 1,
        uuid: 'uuid-updated',
        name: 'asset-updated',
    },
],{
    // updateOnDuplicate: ['name'],
});

To Reproduce
Steps to reproduce the behavior:

1. Define model Asset:

Asset.init(
	{
		id: {
			type: Sequelize.INTEGER,
			primaryKey: true,
		},
		uuid: {
			type: Sequelize.UUID,
		},
		name: {
			type: Sequelize.STRING,
			allowNull: false,
		},
	},
	{
		sequelize,
	}
);

2. Run the code above
3. See a SequelizeUniqueConstraintError

What do you expect to happen?

I wanted

const assets = await Asset.findAll({ where: {} });
console.log(assets.map(a => a.toJSON()));

to produce:

[ { id: 1,
    uuid: 'uuid-updated',
    name: 'asset-updated',
    createdAt: 2019-06-20T13:04:53.000Z,
    updatedAt: 2019-06-20T13:04:53.000Z },
  { id: 2,
    uuid: 'uuid-2',
    name: 'asset-2',
    createdAt: 2019-06-20T13:04:53.000Z,
    updatedAt: 2019-06-20T13:04:53.000Z } ]

What is actually happening?

The mentioned code produces

SequelizeUniqueConstraintError: Validation error
      at Query.formatError (node_modules/sequelize/lib/dialects/mysql/query.js:218:16)
      at Query.handler [as onResult] (node_modules/sequelize/lib/dialects/mysql/query.js:46:23)
      at Query.execute (node_modules/mysql2/lib/commands/command.js:30:14)
      at Connection.handlePacket (node_modules/mysql2/lib/connection.js:449:32)
      at PacketParser.Connection.packetParser.p [as onPacket] (node_modules/mysql2/lib/connection.js:72:12)
      at PacketParser.executeStart (node_modules/mysql2/lib/packet_parser.js:75:16)
      at Socket.Connection.stream.on.data (node_modules/mysql2/lib/connection.js:79:25)
      at addChunk (_stream_readable.js:263:12)
      at readableAddChunk (_stream_readable.js:250:11)
      at Socket.Readable.push (_stream_readable.js:208:10)
      at TCP.onread (net.js:594:20)

The output is as expected if I pass updateOnDuplicate: ['name', 'uuid'] as option to Asset.bulkCreate, but I want the option to default to that by itself.

Environment

Dialect:

• mysql
• postgres
• sqlite
• mssql
• any
  Dialect library version: "mysql2": "1.6.5"
  Database version: 5.7.23
  Sequelize version: "5.8.7"
  Node Version: "8.9.3"
  OS: Linux
  Tested with latest release:
• No
• Yes, specify that version:

Start by reproducing the example through the Asset.bulkCreate entry point against MySQL 5.7, then inspect how updateOnDuplicate is handled for the MySQL dialect. Add regression coverage for the default behavior and verify that the duplicate primary-key row is updated without explicitly supplying the option.