Migrate pieces of x/genutil missed in #6734 (#6860)

* Migrate pieces of x/genutil missed in 6734

* Fix tests

* Fix lint

* Add test

x/auth/tx/builder.go

@@ -60,6 +60,10 @@ func newBuilder(pubkeyCodec types.PublicKeyCodec) *builder {
 }
 
 func (t *builder) GetMsgs() []sdk.Msg {
+	if t.tx == nil || t.tx.Body == nil {
+		return nil
+	}
+
 	anys := t.tx.Body.Messages
 	res := make([]sdk.Msg, len(anys))
 	for i, any := range anys {

x/auth/tx/builder_test.go

@@ -110,6 +110,11 @@ func TestTxBuilder(t *testing.T) {
 	require.Equal(t, len(msgs), len(tx.GetMsgs()))
 	require.Equal(t, 1, len(tx.GetPubKeys()))
 	require.Equal(t, pubkey.Bytes(), tx.GetPubKeys()[0].Bytes())
+
+	tx = &builder{}
+	require.NotPanics(t, func() {
+		_ = tx.GetMsgs()
+	})
 }
 
 func TestBuilderValidateBasic(t *testing.T) {