Code improvements

app/Models/User.php

@@ -2,7 +2,7 @@
 
 namespace App\Models;
 
-use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Foundation\Auth\User as Authenticatable;
 use Illuminate\Notifications\Notifiable;
 
@@ -115,10 +115,10 @@ class User extends Authenticatable
     }
 
     public function localGroup() : Tenant {
-        return $this->belongsTo(Tenant::class, 'local_group', 'slug')->first();
+        return $this->belongsTo(Tenant::class, 'local_group', 'slug')->firstOrFail();
     }
 
-    public function costUnits()
+    public function costUnits() : BelongsToMany
     {
         return $this->belongsToMany(CostUnit::class, 'cost_unit_treasurers', 'user_id', 'cost_unit_id')
             ->withTimestamps();