Eval Populate fails with SQL Error on Radio Button Element

[JimKeaneUoH]

Prior to 3.9.2 the below used to work but now fails with an SQL null error:

$array_value = '{verbalr___get_questions}';
$local_array = explode(",", $array_value);
$question_number = $local_array[0];
$db = JFactory::getDbo();
$query = "SELECT label_1, value_1, label_2, value_2, label_3, value_3, label_4, value_4 FROM question_bank WHERE id = " . $question_number;
$db->setQuery($query);
$rows = $db->loadAssocList();

$options[] = JHTML::_('select.option', $rows[0]['value_1'], $rows[0]['label_1']);
$options[] = JHTML::_('select.option', $rows[0]['value_2'], $rows[0]['label_2']);
$options[] = JHTML::_('select.option', $rows[0]['value_3'], $rows[0]['label_3']);
$options[] = JHTML::_('select.option', $rows[0]['value_4'], $rows[0]['label_4']);

return $options;

{verbalr___get_questions} is populated via the form PHP Plugin onBeforeLoad successfully.

On working through this error it turned out that the data for {verbalr___get_questions} was not available to the Radio button element's Eval Populate at the time it ran. I got around this by getting the value using $this->getFormModel instead as so:
$array_value = $this->getFormModel()->data['verbalr___get_questions'];

However, this now fails on submit as $this->getFormModel is not available on submit, which leads me to this inelegant dual method which does work:

$array_value_form = '{verbalr___get_questions}';
$array_value_direct = $this->getFormModel()->data['verbalr___get_questions'];
if ($array_value_form == ''){$array_value = $array_value_direct;} else {$array_value = $array_value_form;}

I'm guessing this is a bug, and that my original implementation should have continued to work following the update.