MyModule.sol

MyModule.sol

pragma solidity ^0.8.6;

import "@gnosis.pm/zodiac/contracts/core/Module.sol";
import "./Button.sol";

contract MyModule is Module {
    address public button;
    

    function pushButton() external {
        exec(
            button,
            0,
            abi.encodePacked(bytes4(keccak256("pushButton()"))),
            Enum.Operation.Call
        );
    }
    
    constructor(address _owner, address _button) {
        bytes memory initializeParams = abi.encode(_owner, _button);
        setUp(initializeParams);
    }

    /// @dev Initialize function, will be triggered when a new proxy is deployed
    /// @param initializeParams Parameters of initialization encoded
    function setUp(bytes memory initializeParams) public override initializer {
        __Ownable_init();
        (address _owner, address _button) = abi.decode(initializeParams, (address, address));

        setAvatar(_owner);
        setTarget(_owner);
        button = _button;
        transferOwnership(_owner);
    }
}

Deploying this contract fails with the error reverted with reason string 'Initializable: contract is not initializing' unless the initializer modifier is added to the setUp function on line 26.

Thanks, @Geimaj! Have updated the gist.