Revert "Merge pull request #3079 from soyuka/feature/empty-item-operations"

This reverts commit c277aeb8c67bff72188aa65ce896bc3b1f08c468, reversing
changes made to 1088a5d26b298d5b6130da24af35124e0b3cab00.

Author: teohhanhui

SchemaFactory.php

@@ -230,7 +230,7 @@ private function getMetadata(string $resourceClass, string $type = Schema::TYPE_
             $inputOrOutput = $resourceMetadata->getTypedOperationAttribute($operationType, $operationName, $attribute, ['class' => $resourceClass], true);
         }
 
-        if (false === ($inputOrOutput['class'] ?? false)) {
+        if (null === ($inputOrOutput['class'] ?? null)) {
             // input or output disabled
             return null;
         }