NFT restricted access

TokenRestrictedThing.sol

// SPDX-License-Identifier: MIT

pragma solidity 0.8.4;

import 'https://github.com/Rari-Capital/solmate/blob/main/src/tokens/ERC721.sol';

contract Ownable {
    address public owner;

    modifier onlyOwner {
        require(msg.sender == owner, "NOT_OWNER");
        _;
    }
    
    constructor() {
        owner = msg.sender;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        owner = newOwner;
    }
}

contract AccessToken is ERC721("ACCESS", "ACS"), Ownable {
    modifier HasAccessToken {
        require(balanceOf[msg.sender] > 0, "NOT_HOLDER");
        _;
    }

    function mint(address to, uint256 id) public onlyOwner {
        _mint(to, id);
    }

    function tokenURI(uint256) public override pure returns (string memory) {
        return "PLACEHOLDER";
    }
}

/// @notice This is an NFT restricted contract.
contract TokenRestrictedThing is AccessToken {
    uint256 public counter = 1;

    function doThing() public HasAccessToken {
        counter++;
    }
}