Always pass $key to NullAdapter->createCacheItem

Previously, if this were called, it would throw an ArgumentCountError.
I'm assuming existing code always checks hasItem, so this bug hasn't impacted many people.
This was noticed via static analysis.

The get() method was added to NullAdapter in symfony 4.2

src/Symfony/Component/Cache/Adapter/NullAdapter.php

@@ -42,7 +42,7 @@ function ($key) {
      */
     public function get(string $key, callable $callback, float $beta = null, array &$metadata = null)
     {
-        return $callback(($this->createCacheItem)());
+        return $callback(($this->createCacheItem)($key));
     }
 
     /**

src/Symfony/Component/Cache/Tests/Adapter/NullAdapterTest.php

@@ -34,6 +34,19 @@ public function testGetItem()
         $this->assertNull($item->get(), "Item's value must be null when isHit is false.");
     }
 
+    public function testGet()
+    {
+        $adapter = $this->createCachePool();
+
+        $fetched = [];
+        $item = $adapter->get('myKey', function ($item) use (&$fetched) { $fetched[] = $item; });
+        $this->assertCount(1, $fetched);
+        $item = $fetched[0];
+        $this->assertFalse($item->isHit());
+        $this->assertNull($item->get(), "Item's value must be null when isHit is false.");
+        $this->assertSame('myKey', $item->getKey());
+    }
+
     public function testHasItem()
     {
         $this->assertFalse($this->createCachePool()->hasItem('key'));