Updated AbstractTest.php

Fixed deprecation warning

Author: sorinsarca

tests/AbstractTest.php

@@ -72,7 +72,7 @@ protected static function parserVocabulary(): ?Vocabulary
     /**
      * @dataProvider draftValidationsProvider
      */
-    public function testValidations(string $uri, $data, bool $valid, bool $expectException = false, array $globals = null, array $slots = null, array $skip_drafts = null)
+    public function testValidations(string $uri, $data, bool $valid, bool $expectException = false, ?array $globals = null, ?array $slots = null, ?array $skip_drafts = null)
     {
         $validator = self::validator();
 
@@ -120,4 +120,4 @@ public function draftValidationsProvider(): iterable
      * @return array
      */
     abstract public function validationsProvider(): array;
-}
+}