How do you validate a fieldset with js? – Blancer.com Tutorials and projects

So at the time I try to validate a fieldset of radio buttons where the user have to check their sex. Because I’m new to js and I don’t find anything useful when I google I ask here.

So this is my code: HTML

 <body>
    <div id="popupKontakt" class="clearfix,">
        <section id="kontakt">
            <div class="intro-container">
                <h1>Kontakt</h1>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Saepe commodi, quod, quisquam cum ea itaque dolore eum sunt ipsam deleniti rerum qui nemo inventore ab? Commodi, voluptates. Aspernatur, neque nesciunt.</p>
            </div>
            <form id="kontakt-form" name="Kontakt-form" onsubmit="return validation()" >
                <div class="Container">
                    <div class="row">
                    <fieldset name="geschlecht">
                        <legend>Wählen Sie Ihr Geschlecht:</legend>
                        <div>
                            <input type="radio" id="Maennlich" name="Maennlich" value="Maennlich" />
                            <label for="Maennlich">Männlich</label>
                        </div>

                        <div>
                            <input type="radio" id="Weiblich" name="Weiblich" value="Weiblich" />
                            <label for="Weiblich">Weiblich</label>
                        </div>

                        <div>
                            <input type="radio" id="Divers" name="Divers" value="Divers" />
                            <label for="Divers">Divers</label>
                        </div>
                    </fieldset>

and here the js:

function validation() {
    let geschlecht = document.forms["Kontakt-form"]["geschlecht"].value;
    console.log(geschlecht);
    if (Maennlich === null) {
        if (Weiblich === null) {
            if (Divers === null) {
                alert("Bitte geben Sie ihren Namen an");
            }
        }
    }