From b8b01f536f36ddd64d7ca35352cc761c5b5a4810 Mon Sep 17 00:00:00 2001
From: Jared Tobin <jared@jtobin.io>
Date: Fri, 1 May 2026 12:00:19 -0230
Subject: [PATCH] mssmt: guard nil children in BranchNode.Copy

NewComputedBranch creates BranchNode with nil Left/Right children,
which the DB-backed tree stores return during proof construction.
Copy() previously dereferenced these unconditionally, causing a
panic when running mssmt tests against sqlite3/postgres backends.
---
 mssmt/node.go | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mssmt/node.go b/mssmt/node.go
index e29b67f1e4..dab5a8a731 100644
--- a/mssmt/node.go
+++ b/mssmt/node.go
@@ -275,10 +275,22 @@ func (n *BranchNode) Copy() Node {
 		*sumCopy = *n.sum
 	}
 
+	var leftCopy, rightCopy Node
+	if n.Left != nil {
+		leftCopy = NewComputedNode(
+			n.Left.NodeHash(), n.Left.NodeSum(),
+		)
+	}
+	if n.Right != nil {
+		rightCopy = NewComputedNode(
+			n.Right.NodeHash(), n.Right.NodeSum(),
+		)
+	}
+
 	return &BranchNode{
 		nodeHash: nodeHashCopy,
-		Left:     NewComputedNode(n.Left.NodeHash(), n.Left.NodeSum()),
-		Right:    NewComputedNode(n.Right.NodeHash(), n.Right.NodeSum()),
+		Left:     leftCopy,
+		Right:    rightCopy,
 		sum:      sumCopy,
 	}
 }