Scala Writeable of AnyContentAsMultipartFormData - play 2.6

Question

I have those lines in my code

  implicit val anyContentAsMultipartFormWritable: Writeable[AnyContentAsMultipartFormData] = {
    MultipartFormDataWritable.singleton.map(_.mdf)
  }

I had to upgrade my play version from play 2.5 to play 2.6.6, and now those lines are not working. This is the problem:

value mdf is not a member of play.api.mvc.AnyContentAsMultipartFormData

I see that mdf is a member of that class at documentation, and it not seems that this changed in play 2.6.6.

I would appreciate any help.