Let us have an XML structure like this:

<MOODLE_BACKUP>

  <COURSE>

    <FORMATDATA>

      <WEEKS>

        <WEEK>

          <SECTION>1</SECTION>

          <HIDENUMBER>1</HIDENUMBER>

        </WEEK>

      </WEEKS>

    </FORMATDATA>

  </COURSE>

</MOODLE_BACKUP>

Let us parse this XML with our progressive_parser and process it with progressive_parser_processor classes. Let us observe following paths:

$pr->add_path('/MOODLE_BACKUP/COURSE/FORMATDATA', true);

$pr->add_path('/MOODLE_BACKUP/COURSE/FORMATDATA/WEEKS/WEEK');

As you can see, the FORMATDATA elements was requested to be grouped (the second parameter of the add_path() method). To refresh your backup/restore API knowledge, if a path is processed as a grouped one, it is returned in one chunk together with all its subpaths.

Expected behaviour:

We should get an array like FORMATDATA => WEEKS => WEEK[0], WEEK[1], WEEK[2] etc.

Actual behaviour:

PHP error "array_key_exists() expects parameter 2 to be array, null given" when calling build_currentdata() method's code:

if (!array_key_exists($grouped, $this->currentdata)) {

    $a = new stdclass();

    $a->grouped = $grouped;

    $a->child = $data['path'];

    throw new progressive_parser_exception('xml_cannot_add_to_grouped', $a);

}