NULL is coerced to empty string on Instance.update() for DATE field

What you are doing?

Trying to set a field to NULL on update().

User.findOne({ where: { confirmed_token: confirmToken } })
  .then((obj) => {
    const user = obj;

    return user.update({
      confirmed_expires: null,
    }, { fields: ['confirmed_expires'] });
  })

What do you expect to happen?

I would like the value to be updated to NULL

What is actually happening?

The value of confirmed_expires is being set to an empty string when passed to update and then somewhere downstream being set to Invalid Date in the SQL query before entering the DB.

Dialect: mysql
Database version: Ver 14.14 Distrib 5.7.18, for osx10.12
Sequelize version: 4.7.5

Additional Context:

This works just fine. Value is set to NULL as I would expect.

user.confirmed_expires = null;
user.save(['confirmed_expires']);

This does NOT work.

user.confirmed_expires = null;
user.save({fields: ['confirmed_expires']});

My User Model:

const User = sequelize.define('user', {
  confirmed_expires: {
    type: DataTypes.DATE,
    allowNull: true,
    defaultValue: null,
    validate: {
      isDate: true,
      suspicious: (value) => {
        v.suspicious(value);
      },
    },
  },
}, {
  underscored: true,
  deletedAt: 'deleted_at',
  paranoid: true,
});

// Methods
User.prototype.hashPassword = password => bcrypt.hash(password, 10).then(hash => hash);

User.prototype.comparePassword = function comparePassword(userPassword) {
  return bcrypt.compare(userPassword, this.password).then(isMatch => isMatch);
};

module.exports = User;

The problem seems to be that a DATE field, even with allowNull: true and defaultValue: null set, does not accept a null value.

Start at Instance.update() and the DATE field handling described in the report, comparing it with the working user.save(['confirmed_expires']) path. Reproduce the MySQL case with confirmed_expires set to null and verify that the generated SQL preserves NULL rather than converting it to an empty or invalid date.