function validateFollow(
        uint256 profileId,
        address follower,
        uint256 followNFTTokenId
    ) external view override {
        address followNFT = ILensHub(HUB).getFollowNFT(profileId);
        if (followNFT == address(0)) revert Errors.FollowInvalid();
        if (followNFTTokenId == 0) {
            // check that follower owns a followNFT
            if (IERC721(followNFT).balanceOf(follower) == 0) revert Errors.FollowInvalid();
        } else {
            // check that follower owns the specific followNFT
            if (IERC721(followNFT).ownerOf(followNFTTokenId) != follower)
                revert Errors.FollowInvalid();
        }
    }
    function followModuleTransferHook(
        uint256 profileId,
        address from,
        address to,
        uint256 followNFTTokenId
    ) external override {
        address owner = IERC721(HUB).ownerOf(profileId);
        if (!_approvedByProfileByOwner[owner][profileId][to])
            revert Errors.FollowNotApproved();
        _approvedByProfileByOwner[owner][profileId][to] = false; // prevents repeat follows
    }
