Nul pointer

app/Http/Controllers/DnaController.php

@@ -137,14 +137,14 @@ class DnaController extends Controller
             if($status === 'SUBMITTED') $bills = $bills->where('is_submitted', true);
         }
         
-        $bills = $bills->orderBy('created_at', 'DESC')->paginate(20);
+        $bills = $bills->orderBy('effective_date', 'DESC')->paginate(20);
         return view('app.dna.my-bills', compact('bills', 'filters'));
     }
 
     public function myClinicalTeams(Request $request){
         $filters = $request->all();
         $teams = ProTeam::where('assistant_pro_id', $this->performer->pro->id);        
-        $teams = $teams->orderBy('effective_date', 'DESC')->paginate(20);
+        $teams = $teams->orderBy('created_at', 'DESC')->paginate(20);
         return view('app.dna.my-clinical-teams', compact('teams', 'filters'));
     }