Allowed nullable type declarations for method parameters across the codebase

Author: MateuszKolankowski

src/contracts/Exception/InvalidConfigurationException.php

@@ -13,7 +13,7 @@
 
 class InvalidConfigurationException extends Exception
 {
-    public function __construct(string $message = '', int $code = 1, Throwable $previous = null)
+    public function __construct(string $message = '', int $code = 1, ?Throwable $previous = null)
     {
         parent::__construct("Invalid schema configuration: {$message}", $code, $previous);
     }