$ cat x.scala
object Thing {
  /**
   * @usecase def merge[T, List[T]](l: List[T], r: List[T]): List[(Option[T], Option[T])] 
   */
  def merge[T, List[T] <: Traversable[T]](l: List[T], r: List[T])(implicit nth: Nothing): List[(Option[T],Option[T])] = ???
}

$ scaladoc x.scala
x.scala:3: warning: only classes can have declared but undefined members
   * @usecase def merge[T, List[T]](l: List[T], r: List[T]): List[(Option[T], Option[T])] 
              ^
warning: there were 1 feature warning(s); re-run with -feature for details
model contains 2 documentable templates
two warnings found

$ diff y.scala x.scala
3c3
<    * @usecase def merge[T, List[T]](l: List[T], r: List[T]): List[(Option[T], Option[T])] = ??? 
---
>    * @usecase def merge[T, List[T]](l: List[T], r: List[T]): List[(Option[T], Option[T])] 

$ scaladoc y.scala
warning: there were 1 feature warning(s); re-run with -feature for details
model contains 2 documentable templates
one warning found