fix: fix backfill with null tipsets present (#6409)

Author: LesnyRumcajs

CHANGELOG.md

@@ -49,6 +49,8 @@
 
 ### Fixed
 
+- [#6409](https://github.com/ChainSafe/forest/pull/6409) Fixed backfill issue when null tipsets are present.
+
 - [#6327](https://github.com/ChainSafe/forest/pull/6327) Fixed: Forest returns 404 for all invalid api paths.
 
 ## Forest v0.30.5 "Dulce de Leche"

src/tool/subcommands/index_cmd.rs

@@ -99,8 +99,11 @@ impl IndexCommands {
                 println!("Head epoch:    {}", head_ts.epoch());
 
                 let from_ts = if let Some(from) = from {
+                    // ensure from epoch is not greater than head epoch. This can happen if the
+                    // assumed head is actually a null tipset.
+                    let from = std::cmp::min(*from, head_ts.epoch());
                     chain_store.chain_index().tipset_by_height(
-                        *from,
+                        from,
                         head_ts,
                         ResolveNullTipset::TakeOlder,
                     )?