Ensure all properties have a type

Author: nicolas-grekas

Part/AbstractPart.php

@@ -18,7 +18,7 @@
  */
 abstract class AbstractPart
 {
-    private $headers;
+    private Headers $headers;
 
     public function __construct()
     {

Part/TextPart.php

@@ -28,6 +28,7 @@ class TextPart extends AbstractPart
 
     private static array $encoders = [];
 
+    /** @var resource|string|File */
     private $body;
     private ?string $charset;
     private string $subtype;