Delete quiz JSON error if question category deleted

<table class="generaltable">

<thead>

<tr>

<th class="header c0" style="" scope="col">Category</th>

<th class="header c1 lastcol" style="" scope="col">Action</th>

</tr>

</thead>

<tbody><tr class="lastrow">

<td class="cell c0" style="">Default for Test Duplicate</td>

<td class="cell c1 lastcol" style="">This category has been deleted because, after deleting the course, its questions weren't used any more.</td>

</tr>

</tbody>

</table>

[{"error":false,"data":""}]

SyntaxError: Unexpected token < in JSON at position 0

function course_delete_module($cmid, $async = false) {

...

    // Delete activity context questions and question categories.

    question_delete_activity($cm, !$async);