I-130填表問題 - 移民

最近在幫家人辦I-130，底下這一題實在不太理解
這個3-digit code是在綠卡上的，但家人就是沒有綠卡我才要幫他申請XD
所以應該留空就可以了嗎?
不知道是不是我理解錯誤
還是這個是給曾經有過綠卡，現在要再申請一次的人填的
大家都怎麼填呢?
感謝

What was the beneficiary's class of admission?
The beneficiary's class of admission is the 3-digit code for the immigrant
category under which they were granted their permanent resident status.

This code can be found on their Permanent Resident Card and usually consists
of 1 or 2 letters followed by a number.

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