`JdbcDecoder.optionDecoder` should be a `null` test

[oyvindberg]

This looks wrong. it returns None on failures to decode? The correct thing to do here is to first read the raw value from the ResultSet and then call wasNull. I discovered this when I ended up with an NPE :)

  implicit def optionDecoder[A](implicit decoder: JdbcDecoder[A]): JdbcDecoder[Option[A]] =
    JdbcDecoder(rs =>
      int =>
        decoder.decode(int, rs) match {
          case Left(_)      => None
          case Right(value) => Option(value._2)
        }
    )

[oyvindberg]

Oh, and there is another consequence:

Given this code:

    withConnection {
      for {
        _ <-
          sql"""insert into public.pgtestnull("bool", "float4", "float8", "int4", "int8")
          values (${Option.empty[Boolean]}, ${Option.empty[Float]}, ${Option.empty[Double]}, ${Option.empty[Int]}, ${Option.empty[Double]}) 
       """.insert
        _ <-
          sql"""select "bool", "float4", "float8", "int4", "int8" from public.pgtestnull"""
            .query[(Option[Boolean], Option[Float], Option[Double], Option[Int], Option[Long])]
            .selectStream.runHead.map(println)
      } yield ()

    }

valus are correctly stored as null, while we read:

Some((Some(false),Some(0.0),Some(0.0),Some(0),Some(0)))

[karvanit]

This also leads to "interesting" failures when attempting to .map decoders. For example: "SELECT NULL".query[Option[BigDecimal]] works. But "SELECT NULL".query[Option[Wrapped]] fails when we have

implicit val fromJdbc: JdbcDecoder[Wrapped] = JdbcDecoder.bigDecimal.map(bd => Wrapped(bd.toBigInteger))