title: Play Scala & Slick3, got "Column xx cannot be null" error at a column with "NOT NULL DEFAULT CURRENT_TIMESTAMP"
body: <p>I'm creating a web app using Play Framework 2.6 with slick 3.2.1.
  When I try to insert a record into the table "USER", which has created_at column with "NOT NULL DEFAULT CURRENT_TIMESTAMP" (I'm using MySQL), the database throws an error "Column 'created_at' cannot be null".</p>
  
  <p>I know that the SQL generated by slick is wrong. The statement is trying to insert null into the created_at column. What is the proper way to let slick generate SQL that doesn't contain created_at column?</p>
  
  <p><strong>Excerpt of the scala code.</strong></p>
  
  <pre><code>import org.joda.time.DateTime
  
  case class User(
      id: Option[Long],
      accountId: Long,
      name: String,
      description: Option[String] = None,
      createdAt: Option[DateTime: = None,
  )
  
  class UserTable(tag: Tag) extends Table[User](tag, "user") {
    def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
    def accountId = column[Long]("account_id")
    def name = column[String]("name")
    def description = column[Option[String]]("description")
    def createdAt = column[Option[DateTime]]("created_at")
    def * = (id.?, accountId, name, description, createdAt) &lt;&gt; (User.tupled, User.unapply)
  }
  
  object Users extends TableQuery(new UserTable(_)) {
  }
  
  val user = User(None, accountId, name, description)
  val insert = for {
    newId &lt;- (Users returning Users.map(_.id)) += user
  } yield newId
  
  db.run(insert)
  </code></pre>
  
  <p><strong>generated SQL</strong></p>
  
  <pre><code>[debug] s.j.J.statement - Preparing insert statement (returning: id): insert into `user` (`account_id`,`name`,`description`,`created_at`)  values (?,?,?,?)
  
  [debug] s.j.J.parameter - /------+--------+---------+-----------\
  [debug] s.j.J.parameter - | 1    | 2      | 3       | 4         |
  [debug] s.j.J.parameter - | Long | String | VARCHAR | TIMESTAMP |
  [debug] s.j.J.parameter - |------+--------+---------+-----------|
  [debug] s.j.J.parameter - | 1    | user01 | NULL    | NULL      |
  [debug] s.j.J.parameter - \------+--------+---------+-----------/
  </code></pre>