diff --git a/core/blockchain.go b/core/blockchain.go
index bbe2909e162d..0eaa0823197b 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -2584,6 +2584,8 @@ func (bc *BlockChain) UpdateM1() error {
 		if err != nil {
 			return err
 		}
+	} else if stateDB == nil {
+		return errors.New("nil stateDB in UpdateM1")
 	} else {
 		candidates = state.GetCandidates(stateDB)
 	}
diff --git a/eth/api_backend.go b/eth/api_backend.go
index 161ee5ddfb4f..1a9ebc417091 100644
--- a/eth/api_backend.go
+++ b/eth/api_backend.go
@@ -20,7 +20,6 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"math/big"
 	"os"
 	"path/filepath"
@@ -443,7 +442,11 @@ func (b *EthApiBackend) GetVotersRewards(masternodeAddr common.Address) map[comm
 
 	state, err := chain.StateAt(lastCheckpointBlock.Root())
 	if err != nil {
-		fmt.Println("ERROR Trying to getting state at", lastCheckpointNumber, " Error ", err)
+		log.Error("fail to get state in GetVotersRewards", "lastCheckpointNumber", lastCheckpointNumber, "err", err)
+		return nil
+	}
+	if state == nil {
+		log.Error("fail to get state in GetVotersRewards", "lastCheckpointNumber", lastCheckpointNumber)
 		return nil
 	}
 
@@ -503,7 +506,11 @@ func (b *EthApiBackend) GetVotersCap(checkpoint *big.Int, masterAddr common.Addr
 	state, err := chain.StateAt(checkpointBlock.Root())
 
 	if err != nil {
-		fmt.Println("ERROR Trying to getting state at", checkpoint, " Error ", err)
+		log.Error("fail to get state in GetVotersCap", "checkpoint", checkpoint, "err", err)
+		return nil
+	}
+	if state != nil {
+		log.Error("fail to get state in GetVotersCap", "checkpoint", checkpoint)
 		return nil
 	}
 
@@ -533,9 +540,12 @@ func (b *EthApiBackend) GetEpochDuration() *big.Int {
 func (b *EthApiBackend) GetMasternodesCap(checkpoint uint64) map[common.Address]*big.Int {
 	checkpointBlock := b.eth.blockchain.GetBlockByNumber(checkpoint)
 	state, err := b.eth.blockchain.StateAt(checkpointBlock.Root())
-
 	if err != nil {
-		fmt.Println("ERROR Trying to getting state at", checkpoint, " Error ", err)
+		log.Error("fail to get state in GetMasternodesCap", "checkpoint", checkpoint, "err", err)
+		return nil
+	}
+	if state == nil {
+		log.Error("fail to get state in GetMasternodesCap", "checkpoint", checkpoint)
 		return nil
 	}
 
diff --git a/eth/api_tracer.go b/eth/api_tracer.go
index 01abc14b340f..fbd3bfabd8c6 100644
--- a/eth/api_tracer.go
+++ b/eth/api_tracer.go
@@ -106,6 +106,32 @@ type txTraceTask struct {
 	index   int            // Transaction offset in the block
 }
 
+// blockByNumber is the wrapper of the chain access function offered by the backend.
+// It will return an error if the block is not found.
+func (api *PrivateDebugAPI) blockByNumber(ctx context.Context, number rpc.BlockNumber) (*types.Block, error) {
+	block, err := api.eth.ApiBackend.BlockByNumber(ctx, number)
+	if err != nil {
+		return nil, err
+	}
+	if block == nil {
+		return nil, fmt.Errorf("block #%d not found", number)
+	}
+	return block, nil
+}
+
+// blockByHash is the wrapper of the chain access function offered by the backend.
+// It will return an error if the block is not found.
+func (api *PrivateDebugAPI) blockByHash(ctx context.Context, hash common.Hash) (*types.Block, error) {
+	block, err := api.eth.ApiBackend.BlockByHash(ctx, hash)
+	if err != nil {
+		return nil, err
+	}
+	if block == nil {
+		return nil, fmt.Errorf("block %s not found", hash.Hex())
+	}
+	return block, nil
+}
+
 // TraceChain returns the structured logs created during the execution of EVM
 // between two blocks (excluding start) and returns them as a JSON object.
 func (api *PrivateDebugAPI) TraceChain(ctx context.Context, start, end rpc.BlockNumber, config *TraceConfig) (*rpc.Subscription, error) {
@@ -640,7 +666,7 @@ func (api *PrivateDebugAPI) TraceCall(ctx context.Context, args ethapi.CallArgs,
 		block *types.Block
 	)
 	if hash, ok := blockNrOrHash.Hash(); ok {
-		block, err = api.eth.ApiBackend.BlockByHash(ctx, hash)
+		block, err = api.blockByHash(ctx, hash)
 	} else if number, ok := blockNrOrHash.Number(); ok {
 		if number == rpc.PendingBlockNumber {
 			// We don't have access to the miner here. For tracing 'future' transactions,
@@ -650,7 +676,7 @@ func (api *PrivateDebugAPI) TraceCall(ctx context.Context, args ethapi.CallArgs,
 			// of what the next actual block is likely to contain.
 			return nil, errors.New("tracing on top of pending is not supported")
 		}
-		block, err = api.eth.ApiBackend.BlockByNumber(ctx, number)
+		block, err = api.blockByNumber(ctx, number)
 	} else {
 		return nil, errors.New("invalid arguments; neither block nor hash specified")
 	}
diff --git a/eth/backend.go b/eth/backend.go
index 253d280e046a..f9063d5127e2 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -192,11 +192,14 @@ func New(ctx *node.ServiceContext, config *ethconfig.Config, XDCXServ *XDCx.XDCX
 	eth.txPool = core.NewTxPool(config.TxPool, eth.chainConfig, eth.blockchain)
 	eth.orderPool = core.NewOrderPool(eth.chainConfig, eth.blockchain)
 	eth.lendingPool = core.NewLendingPool(eth.chainConfig, eth.blockchain)
-	if common.RollbackHash != common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000") {
+	if common.RollbackHash != (common.Hash{}) {
 		curBlock := eth.blockchain.CurrentBlock()
+		if curBlock == nil {
+			log.Warn("not find current block when rollback")
+		}
 		prevBlock := eth.blockchain.GetBlockByHash(common.RollbackHash)
 
-		if curBlock.NumberU64() > prevBlock.NumberU64() {
+		if curBlock != nil && prevBlock != nil && curBlock.NumberU64() > prevBlock.NumberU64() {
 			for ; curBlock != nil && curBlock.NumberU64() != prevBlock.NumberU64(); curBlock = eth.blockchain.GetBlock(curBlock.ParentHash(), curBlock.NumberU64()-1) {
 				eth.blockchain.Rollback([]common.Hash{curBlock.Hash()})
 			}
@@ -208,6 +211,8 @@ func New(ctx *node.ServiceContext, config *ethconfig.Config, XDCXServ *XDCx.XDCX
 				log.Crit("Err Rollback", "err", err)
 				return nil, err
 			}
+		} else {
+			log.Error("skip SetHead because target block is nil when rollback")
 		}
 	}
 
diff --git a/eth/hooks/engine_v1_hooks.go b/eth/hooks/engine_v1_hooks.go
index 950e231ba016..65c84d1c30b0 100644
--- a/eth/hooks/engine_v1_hooks.go
+++ b/eth/hooks/engine_v1_hooks.go
@@ -228,11 +228,14 @@ func AttachConsensusV1Hooks(adaptor *XDPoS.XDPoS, bc *core.BlockChain, chainConf
 		)
 
 		stateDB, err := bc.StateAt(bc.GetBlockByHash(block).Root())
-		candidateAddresses = state.GetCandidates(stateDB)
-
 		if err != nil {
 			return nil, err
 		}
+		if stateDB == nil {
+			return nil, errors.New("nil stateDB in HookGetSignersFromContract")
+		}
+
+		candidateAddresses = state.GetCandidates(stateDB)
 		for _, address := range candidateAddresses {
 			v, err := validator.GetCandidateCap(opts, address)
 			if err != nil {
diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index 1f31f604125c..622c297ccadd 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -897,6 +897,10 @@ func (s *PublicBlockChainAPI) GetCandidateStatus(ctx context.Context, coinbaseAd
 			result[fieldSuccess] = false
 			return result, err
 		}
+		if statedb == nil {
+			result[fieldSuccess] = false
+			return result, errors.New("nil statedb in GetCandidateStatus")
+		}
 		candidatesAddresses := state.GetCandidates(statedb)
 		candidates = make([]utils.Masternode, 0, len(candidatesAddresses))
 		for _, address := range candidatesAddresses {
@@ -1052,6 +1056,10 @@ func (s *PublicBlockChainAPI) GetCandidates(ctx context.Context, epoch rpc.Epoch
 			result[fieldSuccess] = false
 			return result, err
 		}
+		if statedb == nil {
+			result[fieldSuccess] = false
+			return result, errors.New("nil statedb in GetCandidates")
+		}
 		candidatesAddresses := state.GetCandidates(statedb)
 		candidates = make([]utils.Masternode, 0, len(candidatesAddresses))
 		for _, address := range candidatesAddresses {
@@ -1305,6 +1313,9 @@ func DoCall(ctx context.Context, b Backend, args CallArgs, blockNrOrHash rpc.Blo
 	if statedb == nil || err != nil {
 		return nil, 0, false, err, nil
 	}
+	if header == nil {
+		return nil, 0, false, errors.New("nil header in DoCall"), nil
+	}
 	if err := overrides.Apply(statedb); err != nil {
 		return nil, 0, false, err, nil
 	}
@@ -1327,6 +1338,9 @@ func DoCall(ctx context.Context, b Backend, args CallArgs, blockNrOrHash rpc.Blo
 	if err != nil {
 		return nil, 0, false, err, nil
 	}
+	if block == nil {
+		return nil, 0, false, fmt.Errorf("nil block in DoCall: number=%d, hash=%s", header.Number.Uint64(), header.Hash().Hex()), nil
+	}
 	author, err := b.GetEngine().Author(block.Header())
 	if err != nil {
 		return nil, 0, false, err, nil
@@ -1948,6 +1962,9 @@ func AccessList(ctx context.Context, b Backend, blockNrOrHash rpc.BlockNumberOrH
 	if err != nil {
 		return nil, 0, nil, err
 	}
+	if block == nil {
+		return nil, 0, nil, fmt.Errorf("nil block in AccessList: number=%d, hash=%s", header.Number.Uint64(), header.Hash().Hex())
+	}
 	author, err := b.GetEngine().Author(block.Header())
 	if err != nil {
 		return nil, 0, nil, err
@@ -3617,10 +3634,16 @@ func GetSignersFromBlocks(b Backend, blockNumber uint64, blockHash common.Hash,
 			if err != nil {
 				return addrs, err
 			}
+			if header == nil {
+				return addrs, errors.New("nil header in GetSignersFromBlocks")
+			}
 			blockData, err := b.BlockByNumber(nil, rpc.BlockNumber(i))
 			if err != nil {
 				return addrs, err
 			}
+			if blockData == nil {
+				return addrs, errors.New("nil blockData in GetSignersFromBlocks")
+			}
 			signTxs := engine.CacheSigningTxs(header.Hash(), blockData.Transactions())
 			for _, signtx := range signTxs {
 				blkHash := common.BytesToHash(signtx.Data()[len(signtx.Data())-32:])