More phpstan checks for better code

tests/unit/Assets/CustomServiceInterface.php

@@ -11,6 +11,7 @@ use phpDocumentor\Reflection\DocBlock\Tags\Factory\StaticMethod;
 
 final class CustomServiceInterface implements Tag
 {
+    /** @var Formatter|null */
     public $formatter;
 
     public function getName() : string
@@ -18,7 +19,7 @@ final class CustomServiceInterface implements Tag
         return 'spy';
     }
 
-    public static function create($body, Formatter $formatter = null)
+    public static function create(string $body, Formatter $formatter = null)
     {
         $tag = new self();
         $tag->formatter = $formatter;