message: Do not allocate empty frozen lists on list freeze
  Summary: I don't expect significant savings from this.
diff: @@ -527,6 +527,13 @@ impl<'v> AValue<'v> for AValueImpl<Direct, ListGen<List<'v>>> {
  freezer: &Freezer,
  ) -> anyhow::Result<FrozenValue> {
  let content = self.1.0.content();
  +
  + if content.is_empty() {
  + let fv = FrozenValue::new_repr(&VALUE_EMPTY_FROZEN_LIST);
  + AValueHeader::overwrite_with_forward::<Self>(me, fv.0.ptr_value());
  + return Ok(fv);
  + }
  +
  let (fv, r, extra) =
  freezer.reserve_with_extra::<AValueImpl<Direct, ListGen<FrozenList>>>(content.len());
  AValueHeader::overwrite_with_forward::<Self>(me, fv.0.ptr_value());
  