- Returns early when there is no Heartwood activation height when creating or updating HistoryTree

- Skips call to `check::legacy_chain()` when no NU5 activation height is set (it would return immediately anyway)
- Replaces `.map()` with `.filter_map()` in `NetworkUpgrade::target_spacings()`
- Removes outdated TODO

zebra-chain/src/history_tree.rs

@@ -428,9 +428,11 @@ impl HistoryTree {
         sapling_root: &sapling::tree::Root,
         orchard_root: &orchard::tree::Root,
     ) -> Result<Self, HistoryTreeError> {
-        let heartwood_height = NetworkUpgrade::Heartwood
-            .activation_height(network)
-            .expect("Heartwood height is known");
+        let Some(heartwood_height) = NetworkUpgrade::Heartwood.activation_height(network) else {
+            // Return early if there is no Heartwood activation height.
+            return Ok(HistoryTree(None));
+        };
+
         match block
             .coinbase_height()
             .expect("must have height")

zebra-chain/src/parameters/network_upgrade.rs

@@ -402,14 +402,10 @@ impl NetworkUpgrade {
             ),
         ]
         .into_iter()
-        .map(move |(upgrade, spacing_seconds)| {
-            let activation_height = upgrade
-                .activation_height(network)
-                .expect("missing activation height for target spacing change");
-
+        .filter_map(move |(upgrade, spacing_seconds)| {
+            let activation_height = upgrade.activation_height(network)?;
             let target_spacing = Duration::seconds(spacing_seconds);
-
-            (activation_height, target_spacing)
+            Some((activation_height, target_spacing))
         })
     }
 

zebra-consensus/src/transaction/check.rs

@@ -356,7 +356,6 @@ pub fn coinbase_expiry_height(
 ) -> Result<(), TransactionError> {
     let expiry_height = coinbase.expiry_height();
 
-    // TODO: replace `if let` with `expect` after NU5 mainnet activation
     if let Some(nu5_activation_height) = NetworkUpgrade::Nu5.activation_height(network) {
         // # Consensus
         //

zebra-state/src/service.rs

@@ -422,11 +422,10 @@ impl StateService {
         tracing::info!("starting legacy chain check");
         let timer = CodeTimer::start();
 
-        if let Some(tip) = state.best_tip() {
-            let nu5_activation_height = NetworkUpgrade::Nu5
-                .activation_height(network)
-                .expect("NU5 activation height is set");
-
+        if let (Some(tip), Some(nu5_activation_height)) = (
+            state.best_tip(),
+            NetworkUpgrade::Nu5.activation_height(network),
+        ) {
             if let Err(error) = check::legacy_chain(
                 nu5_activation_height,
                 any_ancestor_blocks(