Filter::getQuickSearchField

protected function getQuickSearchField()
{
	$result = null;
	if (!empty($this->fields))
	{
		foreach (array_keys($this->fields) as $index)
		{
			$row = $this->fields[$index];
			if (
				(!isset($row['quickSearch']) && !isset($row['quickSearchOnly']))
				|| (isset($row['entity']) && $row['entity'] != 'master')
			)
			{
				continue;
			}
			$result = $row['id'];
		}
		unset($row, $index);
	}
	return $result;
}