php prepared select

Nedenstående kode giver denne fejlmeddelelse knyttet til 'while'-linien:
Fatal error: Call to a member function fetch_assoc() on boolean in ..



$stm_niveau01 ="";
if (isset ($_POST['submit'])) //start POST
{
$stm_niveau01 = htmlentities (trim($_POST['stm_niveau01']), ENT_QUOTES, "utf-8");
         
$sql = "SELECT * FROM stammenu WHERE stm_niveau01 = ?";
$query = $db_link->prepare($sql);
$query->bind_param('s',$stm_niveau01);
$query->execute();
$query->store_result();
$antal = $query->num_rows;           
$result = $query->get_result();   

if ($antal > 0)
{
...
while ($row = $result->fetch_assoc())
{
echo "<tr>";
echo "<td>$row[stm_id]</td>";
echo "<td>$row[stm_niveau01]</td>";
echo "<td>$row[stm_niveau02]</td>";
echo "<td>$row[stm_niveau03]</td>";
echo "<td>$row[stm_niveau04]</td>";
echo "</tr>";
...



$stm_niveau01 modtager den korrekte tekststreng fra $_POST
$antal viser det korrekte antal selekterede records.
Jeg får denne print_r på $query:
mysqli_stmt Object ( [affected_rows] => 6 [insert_id] => 0 [num_rows] => 6 [param_count] => 1 [field_count] => 5 [errno] => 0 [error] => [error_list] => Array ( ) [sqlstate] => 00000 [id] => 1 )