fix(baseapp): allow empty consensus params

CHANGELOG.md

@@ -71,6 +71,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 * (client/keys) [#18562](https://github.com/cosmos/cosmos-sdk/pull/18562) `keys delete` won't terminate when a key is not found
 * (server) [#18537](https://github.com/cosmos/cosmos-sdk/pull/18537) Fix panic when defining minimum gas config as `100stake;100uatom`. Use a `,` delimiter instead of `;`. Fixes the server config getter to use the correct delimiter.
+* [#18531](https://github.com/cosmos/cosmos-sdk/pull/18531) Baseapp's `GetConsensusParams` returns an empty struct instead of panicking if no params are found.
 * (client/tx) [#18472](https://github.com/cosmos/cosmos-sdk/pull/18472) Utilizes the correct Pubkey when simulating a transaction.
 * (baseapp) [#18486](https://github.com/cosmos/cosmos-sdk/pull/18486) Fixed FinalizeBlock calls not being passed to ABCIListeners
 * (baseapp) [#18383](https://github.com/cosmos/cosmos-sdk/pull/18383) Fixed a data race inside BaseApp.getContext, found by end-to-end (e2e) tests.

baseapp/baseapp.go

@@ -522,7 +522,11 @@ func (app *BaseApp) GetConsensusParams(ctx sdk.Context) cmtproto.ConsensusParams
 
 	cp, err := app.paramStore.Get(ctx)
 	if err != nil {
-		panic(fmt.Errorf("consensus key is nil: %w", err))
+		// This could happen while migrating from v0.45/v0.46 to v0.50, we should
+		// allow it to happen so during preblock the upgrade plan can be executed
+		// and the consensus params set for the first time in the new format.
+		app.logger.Error("failed to get consensus params", "err", err)
+		return cmtproto.ConsensusParams{}
 	}
 
 	return cp

baseapp/baseapp_test.go

@@ -720,6 +720,17 @@ func TestGetMaximumBlockGas(t *testing.T) {
 	require.Panics(t, func() { suite.baseApp.GetMaximumBlockGas(ctx) })
 }
 
+func TestGetEmptyConsensusParams(t *testing.T) {
+	suite := NewBaseAppSuite(t)
+	_, err := suite.baseApp.InitChain(&abci.RequestInitChain{})
+	require.NoError(t, err)
+	ctx := suite.baseApp.NewContext(true)
+
+	cp := suite.baseApp.GetConsensusParams(ctx)
+	require.Equal(t, cmtproto.ConsensusParams{}, cp)
+	require.Equal(t, uint64(0), suite.baseApp.GetMaximumBlockGas(ctx))
+}
+
 func TestLoadVersionPruning(t *testing.T) {
 	logger := log.NewNopLogger()
 	pruningOptions := pruningtypes.NewCustomPruningOptions(10, 15)