From 6688301e946b543f8d2677d0a944f9369e578628 Mon Sep 17 00:00:00 2001
From: tersec <tersec@users.noreply.github.com>
Date: Sun, 6 Oct 2024 10:36:53 +0000
Subject: [PATCH] fix adding empty List/HashList to empty HashList (#98)

---
 ssz_serialization/types.nim | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ssz_serialization/types.nim b/ssz_serialization/types.nim
index 35ad090..206e6ce 100644
--- a/ssz_serialization/types.nim
+++ b/ssz_serialization/types.nim
@@ -398,7 +398,9 @@ template len*(a: type HashArray): auto = int(a.maxLen)
 func add*(x: var HashList, val: auto): bool =
   if add(x.data, val):
     x.resizeHashes()
-    clearCaches(x, x.data.len() - 1)
+    if x.data.len() > 0:
+      # Otherwise, adding an empty list to an empty list fails
+      clearCaches(x, x.data.len() - 1)
     true
   else:
     false