diff --git a/src/main/php/org/bovigo/vfs/vfsStream.php b/src/main/php/org/bovigo/vfs/vfsStream.php
index 1eb382d..575b3b9 100644
--- a/src/main/php/org/bovigo/vfs/vfsStream.php
+++ b/src/main/php/org/bovigo/vfs/vfsStream.php
@@ -208,7 +208,7 @@ public static function setup($rootDirName = 'root', $permissions = null, array $
      * @see     https://github.com/mikey179/vfsStream/issues/14
      * @see     https://github.com/mikey179/vfsStream/issues/20
      */
-    public static function create(array $structure, vfsStreamDirectory $baseDir = null)
+    public static function create(array $structure, ?vfsStreamDirectory $baseDir = null)
     {
         if (null === $baseDir) {
             $baseDir = vfsStreamWrapper::getRoot();
@@ -272,7 +272,7 @@ protected static function addStructure(array $structure, vfsStreamDirectory $bas
      * @since   0.11.0
      * @see     https://github.com/mikey179/vfsStream/issues/4
      */
-    public static function copyFromFileSystem($path, vfsStreamDirectory $baseDir = null, $maxFileSize = 1048576)
+    public static function copyFromFileSystem($path, ?vfsStreamDirectory $baseDir = null, $maxFileSize = 1048576)
     {
         if (null === $baseDir) {
             $baseDir = vfsStreamWrapper::getRoot();
@@ -421,7 +421,7 @@ public static function getCurrentGroup()
      * @since   0.10.0
      * @see     https://github.com/mikey179/vfsStream/issues/10
      */
-    public static function inspect(vfsStreamVisitor $visitor, vfsStreamContent $content = null)
+    public static function inspect(vfsStreamVisitor $visitor, ?vfsStreamContent $content = null)
     {
         if (null !== $content) {
             return $visitor->visit($content);