chore: adding defensive check to v7 migrations (#2948)

* adding defensive check to v7 migrations

* adding test coverage for absence of tendermint clients

modules/core/02-client/migrations/v7/store.go

@@ -91,6 +91,10 @@ func handleTendermintMigration(ctx sdk.Context, store sdk.KVStore, cdc codec.Bin
 		return err
 	}
 
+	if len(clients) == 0 {
+		return nil // no-op if no tm clients exist
+	}
+
 	if len(clients) > 1 {
 		return sdkerrors.Wrap(sdkerrors.ErrLogic, "more than one Tendermint client collected")
 	}

modules/core/02-client/migrations/v7/store_test.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/stretchr/testify/suite"
 
-	"github.com/cosmos/ibc-go/v6/modules/core/02-client/migrations/v7"
+	v7 "github.com/cosmos/ibc-go/v6/modules/core/02-client/migrations/v7"
 	"github.com/cosmos/ibc-go/v6/modules/core/02-client/types"
 	host "github.com/cosmos/ibc-go/v6/modules/core/24-host"
 	ibctesting "github.com/cosmos/ibc-go/v6/testing"
@@ -65,6 +65,22 @@ func (suite *MigrationsV7TestSuite) TestMigrateStore() {
 	suite.assertNoLocalhostClients()
 }
 
+func (suite *MigrationsV7TestSuite) TestMigrateStoreNoTendermintClients() {
+	solomachines := []*ibctesting.Solomachine{
+		ibctesting.NewSolomachine(suite.T(), suite.chainA.Codec, "06-solomachine-0", "testing", 1),
+		ibctesting.NewSolomachine(suite.T(), suite.chainA.Codec, "06-solomachine-1", "testing", 4),
+	}
+
+	suite.createSolomachineClients(solomachines)
+	suite.createLocalhostClients()
+
+	err := v7.MigrateStore(suite.chainA.GetContext(), suite.chainA.GetSimApp().GetKey(host.StoreKey), suite.chainA.App.AppCodec(), suite.chainA.GetSimApp().IBCKeeper.ClientKeeper)
+	suite.Require().NoError(err)
+
+	suite.assertSolomachineClients(solomachines)
+	suite.assertNoLocalhostClients()
+}
+
 func (suite *MigrationsV7TestSuite) createSolomachineClients(solomachines []*ibctesting.Solomachine) {
 	// manually generate old protobuf definitions and set in store
 	// NOTE: we cannot use 'CreateClient' and 'UpdateClient' functions since we are