gistfile1.txt

scala> def useInt(i: Int) = println(s"used $i")
useInt: (i: Int)Unit

scala> val i: java.lang.Integer = null
i: Integer = null

// implicit conversion from Integer to Int fails
scala> useInt(i)
java.lang.NullPointerException
at scala.Predef$.Integer2int(Predef.scala:392)

scala> def useOptionInt(o: Option[Int]) = println(s"used $o")
useOptionInt: (o: Option[Int])Unit

scala> val optInteger: Option[java.lang.Integer] = Option(null)
optInteger: Option[Integer] = None

scala> useOptionInt(optInteger)
<console>:16: error: type mismatch;                                                                                                            
found   : Option[Integer]
required: Option[Int]

// implicit conversion still fails, because it happens before the call to Option
scala> useOptionInt(Option(i))
java.lang.NullPointerException
at scala.Predef$.Integer2int(Predef.scala:392)