bin2chen - emissionsToken may be remain in the contract

[sherlock-admin]

bin2chen

medium

emissionsToken may be remain in the contract

Summary

if NullEpoch, emissionsToken will remain in the contract.

Vulnerability Detail

When calling createEpochWithEmissions() to create an epoch, it will transfer the EmissionsToken to the vaults
The code is as follows:

    function createEpochWithEmissions(
        uint256 _marketId,
        uint40 _epochBegin,
        uint40 _epochEnd,
        uint16 _withdrawalFee,
        uint256 _permiumEmissions,
        uint256 _collatEmissions
    ) public returns (uint256 epochId, address[2] memory vaults) {
        // no need for onlyOwner modifier as createEpoch already has modifier
        (epochId, vaults) = createEpoch(
            _marketId,
            _epochBegin,
            _epochEnd,
            _withdrawalFee
        );

        emissionsToken.safeTransferFrom(treasury, vaults[0], _permiumEmissions);  //<-----transfer to vaults[0]
        ICarousel(vaults[0]).setEmissions(epochId, _permiumEmissions);  

        emissionsToken.safeTransferFrom(treasury, vaults[1], _collatEmissions); //<-----transfer to vaults[1]
        ICarousel(vaults[1]).setEmissions(epochId, _collatEmissions);
    }

when the user withdraw() in vaults, the token will be transferred to the user in proportion to the shares.
but the consideration is missing here if no one makes a deposit for this epoch. It will be triggerNullEpoch()
In this case, no one can withdraw(), and the emissionsToken will remain in the contract.
recommended that if NullEpoch, return the emissionsToken to treasury

Impact

emissionsToken may be locked in the contract

Code Snippet

https://github.com/sherlock-audit/2023-03-Y2K/blob/main/Earthquake/src/v2/Carousel/CarouselFactory.sol#L132

Tool used

Manual Review

Recommendation

+    function backEmissionToken(uint256 _id) external       
+                epochIdExists(_id)
+                epochHasEnded(_id)
+                nonReentrant 
+                onlyFactory {
+            if(finalTVL[_id]==0){
+                emissionsToken.safeTransfer(treasury, emissions[_id]);
+            }
+    }

Duplicate of #122