Merge branch '6.4' into 7.0

* 6.4:
  Make more nullable types explicit
  Add more explicit nullable types for default null values

Author: derrabus

Tests/Fixtures/NonTraversableArrayObject.php

@@ -19,7 +19,7 @@ class NonTraversableArrayObject implements \ArrayAccess, \Countable
 {
     private $array;
 
-    public function __construct(array $array = null)
+    public function __construct(?array $array = null)
     {
         $this->array = $array ?: [];
     }

Tests/Fixtures/TraversableArrayObject.php

@@ -19,7 +19,7 @@ class TraversableArrayObject implements \ArrayAccess, \IteratorAggregate, \Count
 {
     private $array;
 
-    public function __construct(array $array = null)
+    public function __construct(?array $array = null)
     {
         $this->array = $array ?: [];
     }