Add more explicit nullable types for default null values

Author: alexandre-daubois

Tests/Fixtures/ContainerAwareFixture.php

@@ -20,7 +20,7 @@ class ContainerAwareFixture implements FixtureInterface, ContainerAwareInterface
 {
     public $container;
 
-    public function setContainer(ContainerInterface $container = null)
+    public function setContainer(?ContainerInterface $container = null)
     {
         $this->container = $container;
     }

Tests/Fixtures/Type/StringWrapper.php

@@ -15,7 +15,7 @@ class StringWrapper
 {
     private $string;
 
-    public function __construct(string $string = null)
+    public function __construct(?string $string = null)
     {
         $this->string = $string;
     }