add null guards in create plan use case

app/Plan/UseCases/CreatePlan.php

@@ -2,6 +2,7 @@
 
 namespace App\Plan\UseCases;
 
+use App\Exceptions\BadRequestException;
 use App\Node\NodeRepository;
 use App\Plan\CreatePlanDto;
 use App\Plan\Plan;
@@ -28,6 +29,18 @@ class CreatePlan
      */
     public function execute(CreatePlanRequest $request): Plan
     {
+        if ($request->userId === null) {
+            throw new BadRequestException('userId is required');
+        }
+
+        if ($request->textId === null) {
+            throw new BadRequestException('textId is required');
+        }
+
+        if ($request->name === null) {
+            throw new BadRequestException('name is required');
+        }
+
         $userId = $request->userId;
         $user = $this->userRepo->find($userId);
         if ($user === null) {