mysqli - Looping under a loop on php not working well

I'm trying to create a table on html from MySQL. I'm trying to run while loop under a while loop. But unfortunately my script has a weird behaviour. It's showing following error and not displaying out put correctly.

Fatal error: Call to a member function fetch_array() on a non-object in /home/windsys/public_html/anamika/test2.php on line 27
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Here is my code. Please tell me what wrong I've done.

<?php
require_once('configuration.php');
$con = new mysqli($hostname, $dbusername, $dbpass, $dbname);
if (mysqli_connect_errno($con)) {
    die('The connection to the database could not be established.');
}

$q2 = "SELECT DISTINCT type FROM product";
$result2 = $con->query($q2);
while ($row2 = $result2->fetch_array()) {
    $type = $row2['type'];
    echo "<tr>
              <td class=\"success\"><b>" . $type . "</b></td>
              <td class=\"success\"></td>
              <td class=\"success\"></td>
              <td class=\"success\"></td>
          </tr>";
    //echo $type."</br>";
    $q1 = "SELECT DISTINCT item_name FROM product WHERE type ='$type'";
    $result = $con->query($q1);
    while ($row = $result->fetch_array()) {
        $item_name = $row['item_name'];
        $item_name = strtolower($item_name);
        $task = "SELECT * FROM product WHERE item_name='$item_name' AND type='$type'";

        $restask = $con->query($task);
        while ($row3 = $restask->fetch_array()) {
            $item_count++;
            $item_cost += $row3['buying_price'];
            //echo $row['buying_price']."</br>";
        }
        echo "<tr><td></td><td>" . $item_name . "</td><td>" . $item_count
            . "</td><td class=\"text-right\">" . $item_cost . "</td></tr>";

        //echo $row['item_name'];
    }
}
?>
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