message: impl Default for FrozenHeapRef
  Summary: Used in the following diff
diff: @@ -33,6 +33,7 @@ use std::{
  use either::Either;
  use gazebo::{cast, prelude::*};
  +use once_cell::sync::Lazy;
  use crate::{
  eval::FrozenDef,
  @@ -128,6 +129,14 @@ where
  {
  }
  +impl Default for FrozenHeapRef {
  + fn default() -> Self {
  + static EMPTY: Lazy<FrozenHeapRef> =
  + Lazy::new(|| FrozenHeapRef(Arc::new(FrozenFrozenHeap::default())));
  + Lazy::force(&EMPTY).dupe()
  + }
  +}
  +
  impl Hash for FrozenHeapRef {
  fn hash<H: Hasher>(&self, state: &mut H) {
  let x: &FrozenFrozenHeap = Deref::deref(&self.0);
  