Fatal error: Uncaught Error: Call to a member function query() on null in

cara mengatasi ini gimana gan Fatal error: Uncaught Error: Call to a member function query() on null in C:\xampp\htdocs\ta\tambahkue.php:245 Stack trace: #0 {main} thrown in C:\xampp\htdocs\ta\tambahkue.php on line 245

ini codingan nya gan

<?php
        if (isset($_POST['save']))
{
    $koneksi->query("INSERT INTO kue(nama,harga,jumlah) VALUES('$_POST[nama]','$_POST[harga]','$_POST[jumlah]')");
    echo "<div class='alert alert-info'>Data Tersimpan</div>";
    echo "<meta http-equiv='refresh' content='l;url=tambahkue.php?halaman=tambahkue'>";
}
?>