Blank/null IATA code isn't unique when added #679 (#681)

tests/AirlineTest.php

@@ -4,6 +4,7 @@ use App\Services\AirlineService;
 
 class AirlineTest extends TestCase
 {
+    /** @var AirlineService */
     protected $airlineSvc;
 
     public function setUp(): void
@@ -14,6 +15,23 @@ class AirlineTest extends TestCase
         $this->airlineSvc = app(AirlineService::class);
     }
 
+    public function testAddAirline()
+    {
+        $attrs = factory(App\Models\Airline::class)->make([
+            'iata' => '',
+        ])->toArray();
+
+        $airline = $this->airlineSvc->createAirline($attrs);
+        $this->assertNotNull($airline);
+
+        // Add another airline, also blank IATA
+        $attrs = factory(App\Models\Airline::class)->make([
+            'iata' => '',
+        ])->toArray();
+        $airline = $this->airlineSvc->createAirline($attrs);
+        $this->assertNotNull($airline);
+    }
+
     /**
      * Try deleting an airline which has flights/other assets that exist
      */