fix explitic nullable issues

Author: tacman

src/Knp/Snappy/AbstractGenerator.php

@@ -65,7 +65,7 @@ abstract class AbstractGenerator implements GeneratorInterface, LoggerAwareInter
      * @param array       $options
      * @param null|array  $env
      */
-    public function __construct($binary, array $options = [], array $env = null)
+    public function __construct($binary, array $options = [], ?array $env = null)
     {
         $this->configure();
 

src/Knp/Snappy/Image.php

@@ -13,7 +13,7 @@ class Image extends AbstractGenerator
     /**
      * {@inheritdoc}
      */
-    public function __construct($binary = null, array $options = [], array $env = null)
+    public function __construct($binary = null, array $options = [], ?array $env = null)
     {
         $this->setDefaultExtension('jpg');
 

src/Knp/Snappy/Pdf.php

@@ -18,7 +18,7 @@ class Pdf extends AbstractGenerator
     /**
      * {@inheritdoc}
      */
-    public function __construct($binary = null, array $options = [], array $env = null)
+    public function __construct($binary = null, array $options = [], ?array $env = null)
     {
         $this->setDefaultExtension('pdf');
         $this->setOptionsWithContentCheck();