Various code cleanup.

app/Models/PiggyBank.php

@@ -26,6 +26,7 @@ use Carbon\Carbon;
 use Crypt;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphMany;
 use Illuminate\Database\Eloquent\SoftDeletes;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
@@ -123,7 +124,7 @@ class PiggyBank extends Model
      * @codeCoverageIgnore
      * Get all of the piggy bank's notes.
      */
-    public function notes()
+    public function notes(): MorphMany
     {
         return $this->morphMany(Note::class, 'noteable');
     }