use existing variable for empty object CID.

chain/gen/genesis/genesis.go

@@ -59,8 +59,6 @@ type GenesisBootstrap struct {
 	Genesis *types.BlockHeader
 }
 
-var EmptyObjCid = cid.Undef
-
 /*
 From a list of parameters, create a genesis block / initial state
 
@@ -127,12 +125,6 @@ func MakeInitialStateTree(ctx context.Context, bs bstore.Blockstore, template ge
 	// Create empty state tree
 	cst := cbor.NewCborStore(bs)
 
-	var err error
-	EmptyObjCid, err = cst.Put(context.TODO(), []struct{}{})
-	if err != nil {
-		return nil, nil, xerrors.Errorf("putting empty object: %w", err)
-	}
-
 	sv, err := state.VersionForNetwork(template.NetworkVersion)
 	if err != nil {
 		return nil, nil, xerrors.Errorf("getting state tree version: %w", err)

chain/gen/genesis/genesis_eth.go

@@ -19,6 +19,7 @@ import (
 	"github.com/filecoin-project/lotus/chain/state"
 	"github.com/filecoin-project/lotus/chain/types"
 	"github.com/filecoin-project/lotus/chain/types/ethtypes"
+	"github.com/filecoin-project/lotus/chain/vm"
 )
 
 // EthNullAddresses are the Ethereum addresses we want to create zero-balanced EthAccounts in.
@@ -45,7 +46,7 @@ func SetupEAM(_ context.Context, nst *state.StateTree, nv network.Version) error
 
 	header := &types.Actor{
 		Code:    codecid,
-		Head:    EmptyObjCid,
+		Head:    vm.EmptyObjectCid,
 		Balance: big.Zero(),
 		Address: &builtin.EthereumAddressManagerActorAddr, // so that it can create ETH0
 	}
@@ -61,7 +62,7 @@ func MakeEthNullAddressActor(av actorstypes.Version, addr address.Address) (*typ
 
 	act := &types.Actor{
 		Code:    actcid,
-		Head:    EmptyObjCid,
+		Head:    vm.EmptyObjectCid,
 		Nonce:   0,
 		Balance: big.Zero(),
 		Address: &addr,