How can I avoid duplication here?

MyImplicits.scala

object MyImplicits {
  
  implicit def fieldString_To_OptionString(duck: {def getValue(): String}): Option[String] = {
    duck match {
      case null => None
      case x => Option(x.getValue())
    }
  }

  implicit def fieldDecimal_To_OptionOfBigDecimal(duck: {def getValue(): java.math.BigDecimal}): Option[BigDecimal] = {
    duck match {
      case null => None
      case x => Option(x.getValue())
    }
  }
  
}

Thanks!
Just one tiny problem with this: fieldDecimal_To_OptionOfBigDecimal converts to java.math.BigDecimal, not the scala BigDecimal..
But I get the idea, and you'll get beer next time we meet ;)

You want the Scala version? In that case, you can't generify it that way. Your output is not the same as your input. You need two type parameters.

ps: yes, beer!!