UninitializedStorage.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Uninitialized {
    address public owner;

    constructor() {
        owner = msg.sender;
    }

    struct St {
        address a;
    }

    function test() external {
        bad();
    }

    function bad() internal returns (St storage ret) {
        ret = ret;
        ret.a = address(0);
    }
}