[6.x] Fix eloquent collection intersect (#30652)

* fix bug #30626

* Update Collection.php

Author: BSN4

src/Illuminate/Database/Eloquent/Collection.php

@@ -315,6 +315,10 @@ public function intersect($items)
     {
         $intersect = new static;
 
+        if (empty($items)) {
+            return $intersect;
+        }
+
         $dictionary = $this->getDictionary($items);
 
         foreach ($this->items as $item) {

tests/Database/DatabaseEloquentCollectionTest.php

@@ -267,6 +267,22 @@ public function testCollectionReturnsDuplicateBasedOnlyOnKeys()
         $this->assertSame([1 => $two, 2 => $three], $duplicates);
     }
 
+    public function testCollectionIntersectWithNull()
+    {
+        $one = m::mock(Model::class);
+        $one->shouldReceive('getKey')->andReturn(1);
+
+        $two = m::mock(Model::class);
+        $two->shouldReceive('getKey')->andReturn(2);
+
+        $three = m::mock(Model::class);
+        $three->shouldReceive('getKey')->andReturn(3);
+
+        $c1 = new Collection([$one, $two, $three]);
+
+        $this->assertEquals([], $c1->intersect(null)->all());
+    }
+
     public function testCollectionIntersectsWithGivenCollection()
     {
         $one = m::mock(Model::class);