Do...while types not treated same as while types

[muglug]

I think there's an issue dealing with the do statement here:

const getSomeParentNode = (element: Element) => {
    let elementParent = element.parentNode;

    if (!elementParent) {
        return null;
    }

    do {
        elementParent = elementParent.parentNode;

        if (!elementParent) {
            return null;
        }
    } while (elementParent !== document.body);

    return elementParent;
};

11: elementParent = elementParent.parentNode;
                                    ^ property `parentNode`. Property cannot be accessed on possibly null value

Whereas the regular while loop version correctly recalculates the type of elementParent at the top of the loop.

const getSomeParentNode = (element: Element) => {
    let elementParent = element.parentNode;

    if (!elementParent) {
        return null;
    }

    while (elementParent !== document.body) {
        elementParent = elementParent.parentNode;

        if (!elementParent) {
            return null;
        }
    } 

    return elementParent;
};