Notice: undefined offset: 0

mau tanya, misalnya saya buat codingan CRUD php (ubah.php) yg terkoneksi database, nah ada error "Notice: Undefined offset: 0". biasanya itu ada kesalahan dari mana aja yaa?

ini fungsi kueri

$id = $_GET["id"];
$students = kueri("SELECT * FROM mahasiswa WHERE id='$id'" )[0];

Ini coding fungsi kueri

$students = kueri("SELECT * FROM mahasiswa");

if(isset($_POST["cari"])) {
	$students = cari($_POST["keyword"]);
}

ini deklarasi fungsi kueri

function kueri($query) {
		global $conn;
		$result = mysqli_query($conn, $query);
		$rows = [];
		while ( $row = mysqli_fetch_assoc($result) ) {
			$rows[] = $row;
		}
		return $rows;
	}

Ini codingan yg salah undefined offset: 0 line 3

<?php
$id = $_GET["id"];
$students = kueri("SELECT * FROM mahasiswa WHERE id='$id'" )[0];

if (isset($_POST['submit'])) {

	if (ubah($_POST) > 0) {
		echo "
			<script>
				alert('Data Berhasil di ubah!');
				document.location.href = 'index.php?menu=dataMahasiswa&id=1';
			</script>
			";
	} else {
		echo "
			<script>
				alert('Data Gagal di ubah!');
				document.location.href = 'index.php?menu=dataMahasiswa&id=1';
			</script>
			";
	}
}
?>

<center>
	<h1>Ubah Data Mahasiswa</h1>
	<div class="col-md-4">
		<form action="" method="POST">
			<input type="hidden" name="id" value="<? $students['id'] ?>">
			<div class="form-group">
				<label for="npm">NPM</label>
				<input type="text" class="form-control" name="npm" id="npm" value="<?= $students['npm']?>">
			</div>
			<div class="form-group">
				<label for="npm">Nama</label>
				<input type="text" class="form-control" name="nama" id="nama" value="<?= $students['nama']?>">
			</div>
			<div class="form-group">
				<label for="npm">Email</label>
				<input type="text" class="form-control" name="email" id="email" value="<?= $students['email']?>">
			</div>
			<div class="form-group">
				<label for="npm">Jurusan</label>
				<input type="text" class="form-control" name="jurusan" id="jurusan" value="<?= $students['jurusan']?>">
			</div>
			<button type="submit" name="submit" class="btn btn-primary">Submit</button>
		</form>
	</div>
</center>

ini gambar hasilnya