From e97d49170bfc925977880c2b1feaf3afcc460ce6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastian=20K=C3=B6cher?= <bkchr@users.noreply.github.com>
Date: Sun, 26 Jul 2020 21:22:35 +0200
Subject: [PATCH] Fix storage_append (#158)

---
 .../runtime/src/validate_block/implementation.rs    | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/cumulus/runtime/src/validate_block/implementation.rs b/cumulus/runtime/src/validate_block/implementation.rs
index 746f06647f..1f66b6279f 100644
--- a/cumulus/runtime/src/validate_block/implementation.rs
+++ b/cumulus/runtime/src/validate_block/implementation.rs
@@ -264,7 +264,18 @@ impl<B: BlockT> Storage for WitnessStorage<B> {
 
 	fn storage_append(&mut self, key: &[u8], value: Vec<u8>) {
 		let value_vec = sp_std::vec![EncodeOpaqueValue(value)];
-		let current_value = self.overlay.entry(key.to_vec()).or_default();
+
+		let overlay = &mut self.overlay;
+		let witness_data = &self.witness_data;
+		let storage_root = &self.storage_root;
+
+		let current_value = overlay.entry(key.to_vec()).or_insert_with(||
+			read_trie_value::<Layout<HashFor<B>>, _>(
+				witness_data,
+				storage_root,
+				key,
+			).ok().flatten()
+		);
 
 		let item = current_value.take().unwrap_or_default();
 		*current_value = Some(