            uint256 compressedEnumIndex = _sliceToUint256(_compressedStateDiffs[stateDiffPtr:stateDiffPtr + _enumerationIndexSize]);
            require(enumIndex == compressedEnumIndex, "rw: enum key mismatch");
            stateDiffPtr += _enumerationIndexSize;
            
            uint8 metadata = uint8(bytes1(_compressedStateDiffs[stateDiffPtr]));
    function verifyCompressedStateDiffs(
        uint256 _numberOfStateDiffs,
        uint256 _enumerationIndexSize,
        bytes calldata _stateDiffs,
        bytes calldata _compressedStateDiffs
    ) external payable onlyCallFrom(address(L1_MESSENGER_CONTRACT)) returns (bytes32 stateDiffHash) {
        // We do not enforce the operator to use the optimal, i.e. the minimally possible _enumerationIndexSize. 
        // We do enforce however, that the _enumerationIndexSize is not larger than 8 bytes long, which is the 
        // maximal ever possible size for enumeration index.
+       require(_enumerationIndexSize != 0, "whatever");
        require(_enumerationIndexSize <= MAX_ENUMERATION_INDEX_SIZE, "enumeration index size is too large");

        ...
