I have a login php file giving me this error "mysqli_stmt_close() expects parameter 1 to be mysqli_stmt, boolean"

I have a login page for a website that is connected to a MySQL database but I'm getting an error when I try to log in to the website. I am also using xampp. The error says "Warning: mysqli_stmt_close() expects parameter 1 to be mysqli_stmt, boolean given in C:\xamppp\htdocs\mitch\login.php on line 86".

This feature is supposed to let you log in based on the username and password in the database it's connected to. I've tried moving the "mysqli_stmt_close($stmt);" statement into different places, commenting it out, and playing around with the syntax.

if(empty($username_err) && empty($password_err)){
    // Prepare a select statement
    $sql = "SELECT id, username, [password] FROM users WHERE username = ?";

    if($stmt = mysqli_prepare($link, $sql)){
        // Bind variables to the prepared statement as parameters
        mysqli_stmt_bind_param($stmt, "s", $param_username);

        // Set parameters
        $param_username = $username;

        // Attempt to execute the prepared statement
        if(mysqli_stmt_execute($stmt)){
            // Store result
            mysqli_stmt_store_result($stmt);

            // Check if username exists, if yes then verify password
            if(mysqli_stmt_num_rows($stmt) == 1){                    
                // Bind result variables
                mysqli_stmt_bind_result($stmt, $id, $username, $hashed_password);
                if(mysqli_stmt_fetch($stmt)){
                    if(password_verify($password, $hashed_password)){
                        // Password is correct, so start a new session
                        session_start();

                        // Store data in session variables
                        $_SESSION["loggedin"] = true;
                        $_SESSION["id"] = $id;
                        $_SESSION["username"] = $username;                            

                        // Redirect user to welcome page
                        header("location: welcome.php");
                    } else{
                        // Display an error message if password is not valid
                        $password_err = "The password you entered was not valid.";
                    }
                }
            } else{
                // Display an error message if username doesn't exist
                $username_err = "No account found with that username.";
            }
        } else{
            echo "Sorry, Please try again.";
        }

   }

*this is the line that is giving me the error *\
mysqli_stmt_close($stmt);

}

mysqli_close($link);

I'm hoping for the login function to work and bring the user to the welcome page