aave-protocol-v2/contracts/libraries/EthAddressLib.sol

// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.8;

library EthAddressLib {

    /**
    * @dev returns the address used within the protocol to identify ETH
    * @return the address assigned to ETH
     */
    function ethAddress() internal pure returns(address) {
        return 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
    }
}