ListFilter::getFieldsToFilter

protected function getFieldsToFilter(array $fields): array
{
	$results = [];
	foreach ($fields as $name => $field)
	{
		// @todo maybe need to set type for fields in prepareFields method?
		if (is_array($field))
		{
			$type = $field['type'] ?? 'string';
		}
		else
		{
			$type = empty($field->getType()) ? 'string' : $field->getType();
		}

		$results[$name] = [
			'type' => $type,
		];
	}

	return $results;
}