diff --git a/application/forms/DimensionsForm.php b/application/forms/DimensionsForm.php
index fbfbbc7..731b696 100644
--- a/application/forms/DimensionsForm.php
+++ b/application/forms/DimensionsForm.php
@@ -79,7 +79,7 @@ public function assemble()
             $allDimensions = $this->cube->listAdditionalDimensions();
 
             $this->addElement('select', 'addDimension', [
-                'options' => [null => $this->translate('+ Add a dimension')] + $allDimensions,
+                'options' => ['' => $this->translate('+ Add a dimension')] + $allDimensions,
                 'class'   => 'autosubmit'
             ]);
         }
diff --git a/library/Cube/Cube.php b/library/Cube/Cube.php
index 1e688f0..0c14b10 100644
--- a/library/Cube/Cube.php
+++ b/library/Cube/Cube.php
@@ -327,10 +327,10 @@ public function listColumns()
 
     /**
      * @param View $view
-     * @param CubeRenderer $renderer
+     * @param ?CubeRenderer $renderer
      * @return string
      */
-    public function render(View $view, CubeRenderer $renderer = null)
+    public function render(View $view, ?CubeRenderer $renderer = null)
     {
         if ($renderer === null) {
             $renderer = $this->getRenderer();
diff --git a/library/Cube/Hook/IcingaDbActionsHook.php b/library/Cube/Hook/IcingaDbActionsHook.php
index 63c24fe..ce12575 100644
--- a/library/Cube/Hook/IcingaDbActionsHook.php
+++ b/library/Cube/Hook/IcingaDbActionsHook.php
@@ -71,10 +71,10 @@ final protected function addActionLink(Url $url, string $title, string $descript
      * Helper method instantiating an Url object
      *
      * @param string $path
-     * @param array $params
+     * @param ?array $params
      * @return Url
      */
-    final protected function makeUrl(string $path, array $params = null): Url
+    final protected function makeUrl(string $path, ?array $params = null): Url
     {
         $url = Url::fromPath($path);
         if ($params !== null) {
diff --git a/library/Cube/Ido/DataView/Hoststatus.php b/library/Cube/Ido/DataView/Hoststatus.php
index 32ee44b..b639495 100644
--- a/library/Cube/Ido/DataView/Hoststatus.php
+++ b/library/Cube/Ido/DataView/Hoststatus.php
@@ -9,7 +9,7 @@
 
 class Hoststatus extends \Icinga\Module\Monitoring\DataView\Hoststatus
 {
-    public function __construct(ConnectionInterface $connection, array $columns = null)
+    public function __construct(ConnectionInterface $connection, ?array $columns = null)
     {
         $this->connection = $connection;
         $this->query = new HoststatusQuery($connection->getResource(), $columns);