address review comments

Author: bishabosha

library/src/scala/runtime/TupleMirror.scala

@@ -4,10 +4,7 @@ package scala.runtime
  *  as we do not need to synthesize an anonymous Mirror class at every callsite.
  */
 final class TupleMirror(arity: Int) extends scala.deriving.Mirror.Product with Serializable:
-  assert(arity > 0) // EmptyTuple is not a valid `MirroredType` for TupleMirror
-
-  override type MirroredMonoType <: NonEmptyTuple
-
+  assert(arity >= 0) // technically could be used for EmptyTuple also, but it has its own singleton mirror.
   final def fromProduct(product: Product): MirroredMonoType =
     if product.productArity != arity then
       throw IllegalArgumentException(s"expected Product with $arity elements, got ${product.productArity}")