DOES::checkPlan

protected function checkPlan($plan, $result)
{
	$codesUsed = array();
	/** @var ToDo $op */
	foreach($plan as $op)
	{
		$code = $op->getCode();

		if(isset($codesUsed[$code]))
		{
			$result->getErrors()->add('CODE_USED_MULTIPLE_TIMES', 'The following code is used more than once: '.$code, static::ERROR_TYPE_PARSE);
		}
		else
		{
			$codesUsed[$code] = true;
		}
	}
}