HList map doesn't like defaults...

gistfile1.txt

scala> val sample = "A" :: 1 :: 2L :: HNil
sample: shapeless.::[String,shapeless.::[Int,shapeless.::[Long,shapeless.HNil]]] = A :: 1 :: 2 :: HNil

scala> object bleh4 extends Poly1 {
     |     implicit val caseInt = at[Int](_.toString);
     |     implicit val caseLong = at[Long](_.toString);
     |     implicit val caseStr = at[String](_.toString);
     |   }
defined module bleh4

scala>   object bleh5 extends Poly1 {
     |     implicit val caseInt = at[Int](_.toString);
     |     implicit val caseLong = at[Long](_.toString);
     |     implicit val caseStr = at[String](_.toString);
     |     implicit def default[T]=at[T](identity)
     |   }
defined module bleh5

scala> sample map bleh4
res11: shapeless.::[bleh4.caseStr.Result,shapeless.::[bleh4.caseInt.Result,shapeless.::[bleh4.caseLong.Result,shapeless.HNil]]] = A :: 1 :: 2 :: HNil

scala> sample map bleh5
<console>:35: error: could not find implicit value for parameter mapper: shapeless.ops.hlist.Mapper[bleh5.type,shapeless.::[String,shapeless.::[Int,shapeless.::[Long,shapeless.HNil]]]]
              sample map bleh5
                     ^