PHP 将重复行插入数据库

我使用以下代码将用户插入到名为“accounts”的表中

session_start(); 
include("include/connect.php");

            //Posted information from the form put into variables
            $username = mysqli_escape_string($conn, $_POST["username"]);
            $email = mysqli_escape_string($conn,$_POST["email"]);
            $password = mysqli_escape_string($conn,$_POST["password_1"]);

            //check if user already exists
            $usernameCheck="SELECT * FROM accounts WHERE username='$username'";

            //query the db
            $usernameResult = mysqli_query($conn, $usernameCheck) or die(mysqli_error($conn));

            //if no users exits then add data
            if(mysqli_num_rows($usernameResult) == 0){
                $AddUser = "INSERT INTO `accounts` (`username`, `email`, `password`) VALUES ('$username', '$email', '$password')";
                $newUserSend = mysqli_query($conn, $AddUser) or die(mysqli_error($conn));
                mysqli_close($conn);
                $_SESSION["user_session"]= $username;

            }

然而，每次运行时，它都会插入一行包含正确数据的行，然后在下面插入一个空白行。例如

ID Name email           password                                                                             
1  test [email protected]   test              
2  

这是发布数据的表单：

<form method="POST" class="signup-form" action="RegisterProcess.php">
                    <h2 class="form-title">Create account</h2>
                    <div class="form-group">
                        <input type="text" value="<?php echo $username; ?>" class="form-input" name="username" placeholder="Your Name" required/>
                    </div>
                    <div class="form-group">
                      <input type="email" value="<?php echo $email; ?>" class="form-input" name="email" placeholder="Your Email Address" required/>
                    </div>
                    <div class="form-group">
                        <input type="password" class="form-input" name="password_1" placeholder="Your Password" required/>
                        <span toggle="#password" class="zmdi zmdi-eye field-icon toggle-password"></span>
                    </div>
                    <div class="form-group">
                        <input type="password" class="form-input" name="password_2" placeholder="Confirm your password" required/>
                        <span toggle="#password" class="zmdi zmdi-eye field-icon toggle-password"></span>
                    </div>
                    <div class="form-group">
                        <input type="submit" class="form-submit" value="Sign up"/>
                    </div>
                </form>