wormhole-circle-integration/evm/src/cross_chain_usdc/CrossChainUSDCImplementation.sol

// SPDX-License-Identifier: Apache 2
pragma solidity ^0.8.13;

import "@openzeppelin/contracts/proxy/ERC1967/ERC1967Upgrade.sol";

import "./CrossChainUSDC.sol";

contract CrossChainUSDCImplementation is CrossChainUSDC {
    function initialize() initializer public virtual {
        // this function needs to be exposed for an upgrade to pass
    }

    modifier initializer() {
        address impl = ERC1967Upgrade._getImplementation();

        require(
            !isInitialized(impl),
            "already initialized"
        );

        setInitialized(impl);

        _;
    }
}