Fix Query\Builder::pluck() with ObjectId as key (#3169)

Conversion of ObjectId to string is done in Laravel

https://github.com/laravel/framework/blob/646520ad682d98b5211c6e26092259cfbe130b5c/src/Illuminate/Collections/Arr.php#L562

---------

Co-authored-by: Jérôme Tamarelle <jerome.tamarelle@mongodb.com>

src/Query/Builder.php

@@ -851,15 +851,6 @@ public function pluck($column, $key = null)
     {
         $results = $this->get($key === null ? [$column] : [$column, $key]);
 
-        // Convert ObjectID's to strings
-        if (((string) $key) === '_id') {
-            $results = $results->map(function ($item) {
-                $item['_id'] = (string) $item['_id'];
-
-                return $item;
-            });
-        }
-
         $p = Arr::pluck($results, $column, $key);
 
         return new Collection($p);

tests/QueryBuilderTest.php

@@ -525,6 +525,17 @@ public function testPluck()
         $this->assertEquals([25], $age);
     }
 
+    public function testPluckObjectId()
+    {
+        $id = new ObjectId();
+        DB::table('users')->insert([
+            ['id' => $id, 'name' => 'Jane Doe'],
+        ]);
+
+        $names = DB::table('users')->pluck('name', 'id')->toArray();
+        $this->assertEquals([(string) $id => 'Jane Doe'], $names);
+    }
+
     public function testList()
     {
         DB::table('items')->insert([