From 443edf278ddd56590775ce2a902ee600345fae94 Mon Sep 17 00:00:00 2001
From: flicker-harmony <vlad@harmony.one>
Date: Fri, 23 Aug 2019 22:16:08 +0300
Subject: [PATCH 1/2] Add nil pointer checks

---
 core/blockchain.go | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/core/blockchain.go b/core/blockchain.go
index 3fd0a9f22..d3125074e 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -816,23 +816,27 @@ const (
 func (bc *BlockChain) Rollback(chain []common.Hash) {
 	bc.mu.Lock()
 	defer bc.mu.Unlock()
-
+	
 	for i := len(chain) - 1; i >= 0; i-- {
 		hash := chain[i]
 
 		currentHeader := bc.hc.CurrentHeader()
-		if currentHeader.Hash() == hash {
+		if currentHeader != nil && currentHeader.Hash() == hash {
 			bc.hc.SetCurrentHeader(bc.GetHeader(currentHeader.ParentHash, currentHeader.Number.Uint64()-1))
 		}
-		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock.Hash() == hash {
+		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && currentFastBlock.Hash() == hash {
 			newFastBlock := bc.GetBlock(currentFastBlock.ParentHash(), currentFastBlock.NumberU64()-1)
-			bc.currentFastBlock.Store(newFastBlock)
-			rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
+			if newFastBlock != nil {
+				bc.currentFastBlock.Store(newFastBlock)
+				rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
+			}
 		}
-		if currentBlock := bc.CurrentBlock(); currentBlock.Hash() == hash {
+		if currentBlock := bc.CurrentBlock(); currentBlock != nil && currentBlock.Hash() == hash {
 			newBlock := bc.GetBlock(currentBlock.ParentHash(), currentBlock.NumberU64()-1)
-			bc.currentBlock.Store(newBlock)
-			rawdb.WriteHeadBlockHash(bc.db, newBlock.Hash())
+			if newBlock != nil {
+				bc.currentBlock.Store(newBlock)
+				rawdb.WriteHeadBlockHash(bc.db, newBlock.Hash())
+			}
 		}
 	}
 }
@@ -1231,21 +1235,24 @@ func (bc *BlockChain) insertChain(chain types.Blocks) (int, []interface{}, []*ty
 			var winner []*types.Block
 
 			parent := bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
-			for !bc.HasState(parent.Root()) {
+			for parent != nil && !bc.HasState(parent.Root()) {
 				winner = append(winner, parent)
 				parent = bc.GetBlock(parent.ParentHash(), parent.NumberU64()-1)
 			}
 			for j := 0; j < len(winner)/2; j++ {
 				winner[j], winner[len(winner)-1-j] = winner[len(winner)-1-j], winner[j]
 			}
-			// Import all the pruned blocks to make the state available
-			bc.chainmu.Unlock()
-			_, evs, logs, err := bc.insertChain(winner)
-			bc.chainmu.Lock()
-			events, coalescedLogs = evs, logs
+			// Prune in case non-empty winner chain
+			if len(winner) > 0 {
+				// Import all the pruned blocks to make the state available
+				bc.chainmu.Unlock()
+				_, evs, logs, err := bc.insertChain(winner)
+				bc.chainmu.Lock()
+				events, coalescedLogs = evs, logs
 
-			if err != nil {
-				return i, events, coalescedLogs, err
+				if err != nil {
+					return i, events, coalescedLogs, err
+				}
 			}
 
 		case err != nil:

From d58651c8eeabcbe6c2668ca40a0861a1861a7614 Mon Sep 17 00:00:00 2001
From: flicker-harmony <vlad@harmony.one>
Date: Fri, 23 Aug 2019 23:10:34 +0300
Subject: [PATCH 2/2] Fix lint

---
 core/blockchain.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/blockchain.go b/core/blockchain.go
index d3125074e..05d4bc4e7 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -816,7 +816,7 @@ const (
 func (bc *BlockChain) Rollback(chain []common.Hash) {
 	bc.mu.Lock()
 	defer bc.mu.Unlock()
-	
+
 	for i := len(chain) - 1; i >= 0; i-- {
 		hash := chain[i]