Set related record id to null if related record is empty

Author: phpfui

Tests/Unit/RecordTest.php

@@ -30,6 +30,6 @@ public function testEmpty() : void
 $this->assertFalse(empty($order->employee_id));
 $order->employee = new \Tests\Fixtures\Record\Employee();
 $this->assertTrue(empty($order->employee));
-$this->assertTrue(empty($order->employee_id));
+$this->assertNull($order->employee_id);
 }
 }

src/PHPFUI/ORM/Record.php

@@ -157,7 +157,7 @@ public function __set(string $field, mixed $value) : void
 {
 if ($value->empty())
 {
-$this->current[$id] = 0;
+$this->current[$id] = static::$fields[$id]->nullable ? null : 0;
 
 return;
 }