Make `in` clause acceptable empty value. 

On QueryDSL, `in` clause ignore empty value naturally.

```scala
{
  val inClauseResults = withSQL {
    select.from(Order as o)
      .where.in(o.id, Seq())
      .orderBy(o.id)
  }.map(Order(o)).list.apply()
  inClauseResults.map(_.id) should equal(List())  // empty result
}
{
  val notInClauseResults = withSQL {
    select.from(Order as o)
      .where.notIn(o.id, Seq())
      .orderBy(o.id)
  }.map(Order(o)).list.apply()
  notInClauseResults.map(_.id) should equal(List(11, 12, 13, 14, 15, 21, 22, 23, 24, 25, 26)) // all results
}
```