Must use nullable types

src/Libero/ruleset.xml

@@ -47,6 +47,7 @@
             <property name="spacesCountAroundEqualsSign" value="0"/>
         </properties>
     </rule>
+    <rule ref="SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue"/>
     <rule ref="SlevomatCodingStandard.TypeHints.ParameterTypeHintSpacing"/>
     <rule ref="SlevomatCodingStandard.TypeHints.ReturnTypeHintSpacing">
         <properties>

tests/cases/php/nullable-type

@@ -0,0 +1,21 @@
+---DESCRIPTION---
+Must use nullable types
+---CONTENTS---
+<?php
+
+declare(strict_types=1);
+
+function foo(Bar $baz = null, int $qux = null) : void
+{
+}
+
+---FIXED---
+<?php
+
+declare(strict_types=1);
+
+function foo(?Bar $baz = null, ?int $qux = null) : void
+{
+}
+
+---