Gas line repair whats the code say

Had one today that had a gas line repair done. Other issues as well but this stuck me as odd and I figured one of you old salts would know.

The question is can a flex line be repaired and be behind a wall seems if it worked loose you would fill the whole wall. See photo. IT will be covered and that is my concern. Question is can the wall be covered and if this is a code violation what is the code number.

Thank you

The Code is so they can have it dealt with for no cost. New construction.

repair gas line.JPG