◯ ４．子Bは登録完了、子Cは登録は可能だが親とリレーションしない

backend/app/Http/Controllers/Api/ChildrenController.php

@@ -119,7 +119,9 @@ class ChildrenController extends Controller {
 
         // 親子関係の上限の場合
         if (!is_null($get->father_id) && null !== ($rel = FatherRelation::where('father_id', $get->father_id)->first())) {
-            if (Father::select('relation_limit')->where('id', $get->father_id)->first()->relation_limit >= FatherRelation::where('father_id', $get->father_id)->count()) {
+            $fa = Father::select('relation_limit')->where('id', $get->father_id)->first();
+            $fr = FatherRelation::where('father_id', $get->father_id)->count();
+            if (null !== $fa && $fr >= $fa->relation_limit) {
                 return ['status_code' => 400, 'error_messages' => ['仮登録の有効期限が切れました。改めて親にお問い合わせいただき、再登録の手続きを行ってください。']];
             }
         }