[12.x] Address Model@relationLoaded when relation is null (#55531)

* address when relation is null

* added tests and return false when $relatedModels is empty

Author: rodrigopedra

src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php

@@ -1088,7 +1088,11 @@ public function relationLoaded($key)
         if ($nestedRelation !== null) {
             $relatedModels = is_iterable($relatedModels = $this->$relation)
                 ? $relatedModels
-                : [$relatedModels];
+                : array_filter([$relatedModels]);
+
+            if (count($relatedModels) === 0) {
+                return false;
+            }
 
             foreach ($relatedModels as $related) {
                 if (! $related->relationLoaded($nestedRelation)) {

tests/Integration/Database/EloquentModelRelationLoadedTest.php

@@ -135,6 +135,21 @@ public function testWhenParentRelationIsASingleInstance()
         $this->assertTrue($model->relationLoaded('two.one'));
         $this->assertTrue($model->two->one->is($one));
     }
+
+    public function testWhenRelationIsNull()
+    {
+        $one = One::query()->create();
+        $two = $one->twos()->create();
+        $three = $two->threes()->create();
+
+        $model = Three::query()
+            ->with('one.twos')
+            ->find($three->id);
+
+        $this->assertTrue($model->relationLoaded('one'));
+        $this->assertNull($model->one);
+        $this->assertFalse($model->relationLoaded('one.twos'));
+    }
 }
 
 class One extends Model