Значение параметра «-» дает пустую строку (HTML PHP)

Question

Я пытаюсь POST выбрать значения из моей формы HTML в базу данных с помощью phpmysqli. Каким-то образом значение «-» получается пустой строкой. Другие значения в порядке. So echo $title со значением "-" = ""; со значением "Dr." = "Dr."

Мой HTML:

<select
                  name="title"
                  class="form-control"
                  style="width: 50%;"
                  required
                >
                  <option value="" disabled selected>Titula</option>
                  <option value="-">-</option>
                  <option value="Dr.">Dr.</option>
                  <option value="Prof. Dr.">Prof. Dr.</option>
                </select>

Мой PHP:

    <?php
$username = $_POST['username'];
$password = PASSWORD_HASH($_POST["password"], PASSWORD_DEFAULT);
$title = $_POST['title'];
$mail = $_POST['mail'];
$phone = $_POST['phone'];
$fname = $_POST['fname'];
$lname = $_POST['lname'];
$birth = $_POST['birth'];
$street = $_POST['street'];
$city = $_POST['city'];
$country = $_POST['country'];
$zip = $_POST['zip'];
$father = $_POST['father'];
$mother = $_POST['mother'];

if (!empty($username) || !empty($password) || !empty($birth) || !empty($title) || !empty($mail) || !empty($phone) || !empty($fname) || !empty($lname) || !empty($street) || !empty($city) || !empty($country) || !empty($zip) || !empty($father) || !empty($mother)) {
 $host = "localhost";
    $dbUsername = "";
    $dbPassword = "";
    $dbname = "";
    //create connection
    $conn = new mysqli($host, $dbUsername, $dbPassword, $dbname);
    mysqli_set_charset($conn,'utf8mb4');
    if (mysqli_connect_error()) {
     die('Connect Error('. mysqli_connect_errno().')'. mysqli_connect_error());
    } else {
     $SELECT = "SELECT mail From users Where mail = ? Limit 1";
     $INSERT = "INSERT Into users (username, password, birth, title, mail, phone, fname, lname, street, city, country, zip, father, mother) values(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
     //Prepare statement
     $stmt = $conn->prepare($SELECT);
     $stmt->bind_param("s", $mail);
     $stmt->execute();
     $stmt->bind_result($mail);
     $stmt->store_result();
     $rnum = $stmt->num_rows;
     if ($rnum==0) {
      $stmt->close();
      $stmt = $conn->prepare($INSERT);
      $stmt->bind_param("ssssssssssssss", $username, $password, $birth, $title, $mail, $phone, $fname, $lname, $street, $city, $country, $zip, $father, $mother);
      $stmt->execute();
      echo "New record inserted sucessfully";
      echo $title; //empty string
      //header('Location: login.html');
     } else {
      echo "Someone already register using this email";
     }
     $stmt->close();
     $conn->close();
    }
} else {
 echo "All field are required";
 die();
}
?>