feat (service/state): If account doesn't exist at given height, fail …

…gracefully (celestiaorg#996)

* feat: if account doesnt exist at given height, fail gracefully

* refactor: instead of returning error, return 0 and log out err on node side

* log: remove prompt to wait for sync as will be resolved by new head determination from syncer

service/state/core_access.go

@@ -9,6 +9,7 @@ import (
 	sdktx "github.com/cosmos/cosmos-sdk/types/tx"
 	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
 	proofutils "github.com/cosmos/ibc-go/v4/modules/core/23-commitment/types"
+	logging "github.com/ipfs/go-log/v2"
 	rpcclient "github.com/tendermint/tendermint/rpc/client"
 	"github.com/tendermint/tendermint/rpc/client/http"
 	"google.golang.org/grpc"
@@ -21,6 +22,8 @@ import (
 	"github.com/celestiaorg/nmt/namespace"
 )
 
+var log = logging.Logger("state")
+
 // CoreAccessor implements Accessor over a gRPC connection
 // with a celestia-core node.
 type CoreAccessor struct {
@@ -157,6 +160,14 @@ func (ca *CoreAccessor) BalanceForAddress(ctx context.Context, addr Address) (*B
 	}
 	// unmarshal balance information
 	value := result.Response.Value
+	// if the value returned is empty, the account balance does not yet exist
+	if len(value) == 0 {
+		log.Errorf("balance for account %s does not exist at block height %d", addr.String(), head.Height)
+		return &Balance{
+			Denom:  app.BondDenom,
+			Amount: sdktypes.NewInt(0),
+		}, nil
+	}
 	coin, ok := sdktypes.NewIntFromString(string(value))
 	if !ok {
 		return nil, fmt.Errorf("cannot convert %s into sdktypes.Int", string(value))