fix: oracle.RewardBallotWinner detect duplicated uumee (#1432)

## Description



---

### Author Checklist

_All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues._

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] added appropriate labels to the PR
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/umee-network/umee/blob/main/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

_All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items._

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed all author checklist items have been addressed
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

util/genmap/list.go

@@ -0,0 +1,11 @@
+package genmap
+
+// Contains returns true if x is in ls
+func Contains[T comparable](x T, ls []T) bool {
+	for i := range ls {
+		if ls[i] == x {
+			return true
+		}
+	}
+	return false
+}

x/oracle/keeper/reward.go

@@ -5,9 +5,21 @@ import (
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
 
+	"github.com/umee-network/umee/v3/util/genmap"
 	"github.com/umee-network/umee/v3/x/oracle/types"
 )
 
+// prependUmeeIfUnique pushs `uumee` denom to the front of the list, if it is not yet included.
+func prependUmeeIfUnique(voteTargets []string) []string {
+	if genmap.Contains(types.UmeeDenom, voteTargets) {
+		return voteTargets
+	}
+	rewardDenoms := make([]string, len(voteTargets)+1)
+	rewardDenoms[0] = types.UmeeDenom
+	copy(rewardDenoms[1:], voteTargets)
+	return rewardDenoms
+}
+
 // RewardBallotWinners is executed at the end of every voting period, where we
 // give out a portion of seigniorage reward(reward-weight) to the oracle voters
 // that voted correctly.
@@ -18,15 +30,6 @@ func (k Keeper) RewardBallotWinners(
 	voteTargets []string,
 	ballotWinners []types.Claim,
 ) {
-	rewardDenoms := make([]string, len(voteTargets)+1)
-	rewardDenoms[0] = types.UmeeDenom
-
-	i := 1
-	for _, denom := range voteTargets {
-		rewardDenoms[i] = denom
-		i++
-	}
-
 	// sum weight of the claims
 	var ballotPowerSum int64
 	for _, winner := range ballotWinners {
@@ -39,8 +42,8 @@ func (k Keeper) RewardBallotWinners(
 	}
 
 	distributionRatio := sdk.NewDec(votePeriod).QuoInt64(rewardDistributionWindow)
-
 	var periodRewards sdk.DecCoins
+	rewardDenoms := prependUmeeIfUnique(voteTargets)
 	for _, denom := range rewardDenoms {
 		rewardPool := k.GetRewardPool(ctx, denom)
 

x/oracle/keeper/reward_unit_test.go

@@ -0,0 +1,25 @@
+package keeper
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPrependUmeeIfUnique(t *testing.T) {
+	require := require.New(t)
+	tcs := []struct {
+		in  []string
+		out []string
+	}{
+		// Should prepend "uumee" to a slice of denoms, unless it is already present.
+		{[]string{}, []string{"uumee"}},
+		{[]string{"a"}, []string{"uumee", "a"}},
+		{[]string{"x", "a", "heeeyyy"}, []string{"uumee", "x", "a", "heeeyyy"}},
+		{[]string{"x", "a", "uumee"}, []string{"x", "a", "uumee"}},
+	}
+	for i, tc := range tcs {
+		require.Equal(tc.out, prependUmeeIfUnique(tc.in), i)
+	}
+
+}