Upgrade phpstan (#1458)

* Upgrade phpstan

* Remove dead generated code

The isset check ensures that this value is not null or missing.

* Remove dead code

* Fix the case when calling the fixCs method

Author: stof

src/Input/BatchWriteItemInput.php

@@ -71,7 +71,7 @@ public function __construct(array $input = [])
     {
         if (isset($input['RequestItems'])) {
             $this->requestItems = [];
-            foreach ($input['RequestItems'] ?? [] as $key => $item) {
+            foreach ($input['RequestItems'] as $key => $item) {
                 $this->requestItems[$key] = array_map([WriteRequest::class, 'create'], $item);
             }
         }