Error : mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given

Halo kak, dapet error simple tapi ga nemu nemu nih jawabannya, mau $_GET by id tapi ga muncul muncul, udah buka pertanyaan-pertanyaan terkait di forum ini maupun luar, tetep ga nemu solusinya

muncul warning "mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given"

syntax yg error ny kyk gini ::

<?php
$idBiodata = $_GET['idBiodata'];
$query = mysqli_query($conn, "SELECT * FROM biodatasiswa where idBiodata='$idBiodata'");
$a = mysqli_fetch_array($query)
?>

$conn

$conn = mysqli_connect('localhost','root','','siswa_baru');

$_GET

<td style="text-align: center;"><a href="edit-siswa.php?idBiodata=$a['idBiodata']?>">Ubah</a></td>
<td style="text-align: center;"><a href="detail-siswa.php?idBiodata=$a['idBiodata']?>">Detail</a></td>

udah cek koneksi bener, query udah aman, udah coba tambah MYSQLI_ASSOC/NUM/BOTH/free juga ga berhasil, tapi masih belum nemu nih.. mohon dibantu kak