MAGETWO-88631: Pr sprint 10 delivery

- fix tests
- refactor

Author: cpartica

app/code/Magento/GraphQl/Controller/HttpRequestProcessor.php

@@ -22,7 +22,7 @@ class HttpRequestProcessor
     /**
      * @param HttpHeaderProcessorInterface[] $graphQlHeaders
      */
-    public function __construct(array $graphQlHeaders)
+    public function __construct(array $graphQlHeaders = [])
     {
         $this->headerProcessors = $graphQlHeaders;
     }

dev/tests/integration/testsuite/Magento/GraphQl/Controller/GraphQlControllerTest.php

@@ -17,7 +17,7 @@
  * Tests the dispatch method in the GraphQl Controller class using a simple product query
  *
  * @magentoAppArea graphql
- * @magentoDataFixture Magento/Catalog/_files/product_without_options.php
+ * @magentoDataFixture Magento/Catalog/_files/product_simple_with_url_key.php
  */
 
 class GraphQlControllerTest extends \PHPUnit\Framework\TestCase
@@ -50,20 +50,20 @@ protected function setUp()
     }
 
     /**
-     *  Tests if a graphql schema is generated and request is dispatched and response generated
+     * Tests if a graphql schema is generated and request is dispatched and response generated
      */
     public function testDispatch()
     {
         /** @var ProductRepositoryInterface $productRepository */
         $productRepository = $this->objectManager->get(ProductRepositoryInterface::class);
 
         /** @var ProductInterface $product */
-        $product = $productRepository->get('simple');
+        $product = $productRepository->get('simple1');
 
         $query
             = <<<QUERY
  {
-           products(filter: {sku: {eq: "simple"}})
+           products(filter: {sku: {eq: "simple1"}})
            {
                items {
                    id
@@ -88,6 +88,7 @@ public function testDispatch()
         $response = $this->graphql->dispatch($request);
         $output = $this->jsonSerializer->unserialize($response->getContent());
         $linkField = $this->metadataPool->getMetadata(ProductInterface::class)->getLinkField();
+        $this->assertTrue(count($output['data']['products']['items']) > 0, 'Products array has items');
         $this->assertEquals($output['data']['products']['items'][0]['id'], $product->getData($linkField));
         $this->assertEquals($output['data']['products']['items'][0]['sku'], $product->getSku());
         $this->assertEquals($output['data']['products']['items'][0]['name'], $product->getName());

lib/internal/Magento/Framework/GraphQl/Config/Element/Argument.php

@@ -159,9 +159,9 @@ public function getDescription() : string
     /**
      * Return defaultValue if argument is a scalar and has a configured defaultValue. Otherwise return an empty string.
      *
-     * @return string
+     * @return string|null
      */
-    public function getDefaultValue() : string
+    public function getDefaultValue() : ?string
     {
         return $this->defaultValue;
     }

lib/internal/Magento/Framework/GraphQl/Schema/Type/Entity/DefaultMapper.php

@@ -20,7 +20,7 @@ class DefaultMapper implements MapperInterface
     /**
      * @param array $map
      */
-    public function __construct(array $map)
+    public function __construct(array $map = [])
     {
         $this->map = $map;
     }