Prevent unintentionally nullable values in doma-kotlin.

[momosetkn]

Until now, runtime error when Bellow code. You can catch the following error at compile time with this pull request.

val nullableEmp : Emp? = null
val stmt = entityql.update(e, nullableEmp).execute()

I fixed only KEntityql and KNativeSql, but maybe other doma-kotlin code requires review.

[nakamura-to]

Good catch! Thanks for your feedback.