public function handleCustomAnswerCheckboxValue(array &$answer_values): ?string 	{ 		$custom_answer_index = $custom_answer_value = null;  		foreach ($answer_values as $key => $answer_value) { 			if (!is_numeric($answer_value)) { 				$custom_answer_index = $key; 				$custom_answer_value = $answer_value; 			} 		}  		if ($custom_answer_index) { 			unset($answer_values[$custom_answer_index]); 		}  		return $custom_answer_value; 	}