Fix generation of arginfo if type is just null

Author: Girgias

build/gen_stub.php

@@ -510,6 +510,10 @@ function(SimpleType $type) {
 
     public function tryToSimpleType(): ?SimpleType {
         $withoutNull = $this->getWithoutNull();
+        /* type has only null */
+        if (count($withoutNull->types) === 0) {
+            return $this->types[0];
+        }
         if (count($withoutNull->types) === 1) {
             return $withoutNull->types[0];
         }

ext/spl/spl_directory_arginfo.h

@@ -257,7 +257,7 @@ ZEND_END_ARG_INFO()
 ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_SplFileObject_hasChildren, 0, 0, IS_FALSE, 0)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_MASK_EX(arginfo_class_SplFileObject_getChildren, 0, 0, MAY_BE_NULL)
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_SplFileObject_getChildren, 0, 0, IS_NULL, 1)
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_SplFileObject_seek, 0, 1, IS_VOID, 0)