How to do it in Thymeleaf?

gistfile1.txt

Data from the database:

5 BMW      Cars
2 Ford     Cars
6 Fun      NULL
1 Chess    Sport
4 Football Sport
3 Rugby    Sport


I'd like to show them as a <select> with <optgroup>'s **without** data transformation:

<select>
    <optgroup label="Cars">
        <option value="5">BMW</option>
        <option value="2">Ford</option>
    </optgroup>
    <option value="6">Fun</option>
    <optgroup label="Sport">
        <option value="1">Chess</option>
        <option value="4">Football</option>
        <option value="3">Rugby</option>
    </optgroup>
</select>