fix a nil pointer issue cased program crash

Signed-off-by: Leo Chen <leo@harmony.one>

node/node.go

@@ -654,7 +654,7 @@ func (node *Node) UpdateStakingList(block *types.Block) error {
 	for i := range txns {
 		txn := txns[i]
 		toAddress := txn.To()
-		if *toAddress != node.StakingContractAddress { //Not a address aimed at the staking contract.
+		if toAddress != nil && *toAddress != node.StakingContractAddress { //Not a address aimed at the staking contract.
 			continue
 		}
 		currentSender, _ := types.Sender(signerType, txn)

node/node_handler.go

@@ -258,6 +258,7 @@ func (node *Node) VerifyNewBlock(newBlock *types.Block) bool {
 // 2. [leader] send new block to the client
 func (node *Node) PostConsensusProcessing(newBlock *types.Block) {
 	if node.Role == BeaconLeader || node.Role == BeaconValidator {
+		utils.GetLogInstance().Info("PostConsensusProcessing", "newBlock", newBlock)
 		node.UpdateStakingList(newBlock)
 	}
 	if node.Consensus.IsLeader {