diff --git a/composer.json b/composer.json
index 515ba74..f0ea461 100644
--- a/composer.json
+++ b/composer.json
@@ -24,7 +24,7 @@
   },
   "require": { "php": ">=5.3.3" },
   "require-dev": {
-    "phpunit/phpunit": "@stable",
+    "phpunit/phpunit": "9.*",
     "phpmd/phpmd": "@stable",
     "friendsofphp/php-cs-fixer": "@stable",
     "phpmetrics/phpmetrics": "@stable",
diff --git a/src/MarkdownExtended/API/Kernel.php b/src/MarkdownExtended/API/Kernel.php
index faec6de..a02249a 100644
--- a/src/MarkdownExtended/API/Kernel.php
+++ b/src/MarkdownExtended/API/Kernel.php
@@ -344,7 +344,7 @@ public static function applyConfig($name, array $params, $default = null)
      */
     protected static function _configRecursiveIterator(
         $type = 'get',
-        $index,
+        $index = 0,
         $value = null,
         $default = null
     ) {
diff --git a/src/MarkdownExtended/Console/Stream.php b/src/MarkdownExtended/Console/Stream.php
index 678306b..b679af4 100644
--- a/src/MarkdownExtended/Console/Stream.php
+++ b/src/MarkdownExtended/Console/Stream.php
@@ -403,7 +403,10 @@ public function getPipedInput()
                     $data .= fgets($this->stdin);
                 }
             }
-            @file_put_contents($this->stdin, '');
+            /*            if (is_file($this->stdin)) {
+                            file_put_contents($this->stdin, '');
+                        }
+            */
         } catch (\Exception $e) {
             $data = null;
         }
diff --git a/src/MarkdownExtended/Util/ContentCollection.php b/src/MarkdownExtended/Util/ContentCollection.php
index 33fd0a0..4b9589f 100644
--- a/src/MarkdownExtended/Util/ContentCollection.php
+++ b/src/MarkdownExtended/Util/ContentCollection.php
@@ -38,7 +38,7 @@ public function __construct(array $data = [])
      *
      * @throws \MarkdownExtended\Exception\UnexpectedValueException it the argument does not implement `\MarkdownExtended\API\ContentInterface`
      */
-    public function append($content)
+    public function append(mixed $content): void
     {
         if (!is_object($content) || !Kernel::valid($content, Kernel::TYPE_CONTENT)) {
             throw new UnexpectedValueException(
@@ -61,7 +61,7 @@ public function append($content)
      *
      * @throws \MarkdownExtended\Exception\UnexpectedValueException it the argument does not implement `\MarkdownExtended\API\ContentInterface`
      */
-    public function offsetSet($index, $content)
+    public function offsetSet(mixed $index, mixed $content): void
     {
         if (!is_object($content) || !Kernel::valid($content, Kernel::TYPE_CONTENT)) {
             throw new UnexpectedValueException(