Notice: Undefined index: address in C:\xampp\htdocs\contact.php on line 21

<?php

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = trim($_POST ["name"]);
    $email = trim($_POST["email"]);
    $message = trim($_POST ["message"]);

    if ($name == "" OR $email == "" or $message == "") {
        echo "You must specify a value for name, email address, and message.";
        exit;
    }

    foreach($_POST as $value ) {
    if( stripos($value, 'Content-Type:') !== FALSE ) {
        echo "There was a problem with the information you entered.";
        exit;
        }

    }

    if ($_POST ["address"] != "") {
        echo "Your form submission has an error.";
        exit;
    }

    require_once("inc/phpmailer/class.phpmailer.php");           
    $mail = new PHPMailer();

    if (!$mail->ValidateAddress($email)){
        echo "You must specify a valid email address";
        exit;
    }

    $email_body = "";
    $email_body = $email_body . "Name: " . $name . "\n";
    $email_body = $email_body . "Email: " . $email . "\n";
    $email_body = $email_body . "Message: " . $message;

    //TODO: SEND EMAIL

    header ("Location: contact.php?status=thanks");
    exit;
    }
?><?php
$pageTitle = "Contact Mike";
$section = "contact";
include('inc/header.php'); ?>

<div class="section page">

    <div class="wrapper">

        <h1>Contact</h1>

<?php if (isset($_GET ["status"]) AND $_GET["status"] == "thanks") { ?> 
<p>Thanks for the email! I'll be in touch shortly.</p>
<?php } else {?>

    <p>I'd love to hear from you! Complete the form to send me an email.</p>

    <form method="post" action="contact.php">

    <table>
        <tr>
            <th>
                <label for="name">Name</label>
            </th>
            <td>
                <input type="text" name="name" id="name">
            </td>
        </tr>

        <tr>
            <th>
                <label for="email">Email</label>
            </th>
            <td>
                <input type="text" name="email" id="email">
            </td>
        </tr>
            <tr>
            <th>
                <label for="message">message</label>
            </th>
            <td>
                <textarea name= "message" id="message"></textarea>
            </td>
        </tr>

        <tr style="display: none;">
            <th>
                <label for="address">Address</label>
            </th>
            <td>
                <input type="address" name="address" id="address">
                <p>Humans (and frogs): please leave this field blank.</p>
            </td>
        </tr>
    </table>
    <input type="submit" value="send">

        </form>
    <?php } ?>
    <div>

</div>

<?php include('inc/footer.php'); ?>