/// @notice Transfers ownership to given account
/// @param _newOwner Address of new owner
function transferOwnership(address _newOwner) external {
    if (owner != msg.sender) revert NotOwner(owner, msg.sender);
    owner = _newOwner;
    emit TransferOwnership(msg.sender, _newOwner);
}
function transferOwnership(address _newOwner) external {
    if (owner != msg.sender) revert NotOwner(owner, msg.sender);
+   require(_newOwner != 0, "Invalid new owner: address(0)");
    owner = _newOwner;
    emit TransferOwnership(msg.sender, _newOwner);
}
