diff --git a/composer.json b/composer.json
index ac08100e2..1dcac5d06 100644
--- a/composer.json
+++ b/composer.json
@@ -88,7 +88,7 @@
     },
     "scripts": {
         "post-create-project-cmd": "bin/grav install",
-        "phpstan": "vendor/bin/phpstan analyse -l 0 -c ./tests/phpstan/phpstan.neon system/src --memory-limit=256M",
+        "phpstan": "vendor/bin/phpstan analyse -l 1 -c ./tests/phpstan/phpstan.neon system/src --memory-limit=256M",
         "test": "vendor/bin/codecept run unit",
         "test-windows": "vendor\\bin\\codecept run unit"
     },
diff --git a/system/src/Grav/Common/GPM/Local/Package.php b/system/src/Grav/Common/GPM/Local/Package.php
index 27be6660f..ff797a78c 100644
--- a/system/src/Grav/Common/GPM/Local/Package.php
+++ b/system/src/Grav/Common/GPM/Local/Package.php
@@ -23,11 +23,11 @@ class Package extends BasePackage
 
         $this->settings = $package->toArray();
 
-        $html_description = \Parsedown::instance()->line($this->description);
-        $this->data->set('slug', $package->slug);
+        $html_description = \Parsedown::instance()->line($this->__get('description'));
+        $this->data->set('slug', $package->__get('slug'));
         $this->data->set('description_html', $html_description);
         $this->data->set('description_plain', strip_tags($html_description));
-        $this->data->set('symlink', is_link(USER_DIR . $package_type . DS . $this->slug));
+        $this->data->set('symlink', is_link(USER_DIR . $package_type . DS . $this->__get('slug')));
     }
 
     /**
diff --git a/system/src/Grav/Common/Page/Medium/AbstractMedia.php b/system/src/Grav/Common/Page/Medium/AbstractMedia.php
index ada87f2c3..636df4c3d 100644
--- a/system/src/Grav/Common/Page/Medium/AbstractMedia.php
+++ b/system/src/Grav/Common/Page/Medium/AbstractMedia.php
@@ -13,6 +13,7 @@ use Grav\Common\Getters;
 use Grav\Common\Grav;
 use Grav\Common\Media\Interfaces\MediaCollectionInterface;
 use Grav\Common\Media\Interfaces\MediaObjectInterface;
+use Grav\Common\Page\Page;
 use Grav\Common\Utils;
 
 abstract class AbstractMedia extends Getters implements MediaCollectionInterface
@@ -166,7 +167,8 @@ abstract class AbstractMedia extends Getters implements MediaCollectionInterface
     protected function orderMedia($media)
     {
         if (null === $this->media_order) {
-            $page = Grav::instance()['pages']->get($this->path);
+            /** @var Page $page */
+            $page = Grav::instance()['pages']->get($this->__get('path'));
 
             if ($page && isset($page->header()->media_order)) {
                 $this->media_order = array_map('trim', explode(',', $page->header()->media_order));
diff --git a/system/src/Grav/Common/Page/Medium/ImageMedium.php b/system/src/Grav/Common/Page/Medium/ImageMedium.php
index bae243102..515232326 100644
--- a/system/src/Grav/Common/Page/Medium/ImageMedium.php
+++ b/system/src/Grav/Common/Page/Medium/ImageMedium.php
@@ -408,7 +408,7 @@ class ImageMedium extends Medium
         }
 
         if ($width && $height) {
-            $this->cropResize($width, $height);
+            $this->__call('cropResize', [$width, $height]);
         }
 
         return parent::lightbox($width, $height, $reset);
@@ -418,7 +418,7 @@ class ImageMedium extends Medium
      * Sets or gets the quality of the image
      *
      * @param  int $quality 0-100 quality
-     * @return Medium
+     * @return int|$this
      */
     public function quality($quality = null)
     {
diff --git a/system/src/Grav/Common/Page/Medium/Medium.php b/system/src/Grav/Common/Page/Medium/Medium.php
index 9d07d39bd..3afe687ca 100644
--- a/system/src/Grav/Common/Page/Medium/Medium.php
+++ b/system/src/Grav/Common/Page/Medium/Medium.php
@@ -413,6 +413,8 @@ class Medium extends Data implements RenderableInterface, MediaObjectInterface
             case 'source':
                 $element = $this->sourceParsedownElement($attributes, false);
                 break;
+            default:
+                $element = [];
         }
 
         if ($reset) {
diff --git a/system/src/Grav/Common/Twig/Twig.php b/system/src/Grav/Common/Twig/Twig.php
index 4c7ea6351..ba682a76b 100644
--- a/system/src/Grav/Common/Twig/Twig.php
+++ b/system/src/Grav/Common/Twig/Twig.php
@@ -268,6 +268,7 @@ class Twig
 
         $local_twig = clone $this->twig;
 
+        $output = '';
         try {
             // Process Modular Twig
             if ($item->modularTwig()) {
diff --git a/system/src/Grav/Common/User/Group.php b/system/src/Grav/Common/User/Group.php
index d1901496f..9815c0e5e 100644
--- a/system/src/Grav/Common/User/Group.php
+++ b/system/src/Grav/Common/User/Group.php
@@ -89,14 +89,14 @@ class Group extends Data
         $blueprints = new Blueprints();
         $blueprint = $blueprints->get('user/group');
 
-        $config->set("groups.{$this->groupname}", []);
+        $config->set("groups.{$this->get('groupname')}", []);
 
         $fields = $blueprint->fields();
         foreach ($fields as $field) {
             if ($field['type'] === 'text') {
                 $value = $field['name'];
                 if (isset($this->items['data'][$value])) {
-                    $config->set("groups.{$this->groupname}.{$value}", $this->items['data'][$value]);
+                    $config->set("groups.{$this->get('groupname')}.{$value}", $this->items['data'][$value]);
                 }
             }
             if ($field['type'] === 'array' || $field['type'] === 'permissions') {
@@ -105,7 +105,7 @@ class Group extends Data
 
                 if ($arrayValues) {
                     foreach ($arrayValues as $arrayIndex => $arrayValue) {
-                        $config->set("groups.{$this->groupname}.{$value}.{$arrayIndex}", $arrayValue);
+                        $config->set("groups.{$this->get('groupname')}.{$value}.{$arrayIndex}", $arrayValue);
                     }
                 }
             }
diff --git a/system/src/Grav/Framework/Flex/Flex.php b/system/src/Grav/Framework/Flex/Flex.php
index c8278e9af..49fd2b2f7 100644
--- a/system/src/Grav/Framework/Flex/Flex.php
+++ b/system/src/Grav/Framework/Flex/Flex.php
@@ -221,6 +221,7 @@ class Flex implements \Countable
             foreach ($keys as $key) {
                 $flexKey = $guessed[$key] ?? $key;
                 if (\is_array($flexKey)) {
+                    $result = null;
                     foreach ($flexKey as $tryKey) {
                         if ($result = $list[$tryKey] ?? null) {
                             // Use the first matching object (conflicting objects will be ignored for now).
diff --git a/system/src/Grav/Framework/Flex/FlexIndex.php b/system/src/Grav/Framework/Flex/FlexIndex.php
index c31930ad7..bd8762eed 100644
--- a/system/src/Grav/Framework/Flex/FlexIndex.php
+++ b/system/src/Grav/Framework/Flex/FlexIndex.php
@@ -328,7 +328,7 @@ class FlexIndex extends ObjectIndex implements FlexCollectionInterface, FlexInde
                 $debugger->addException($e);
             }
 
-            if (null === $result) {
+            if (!isset($result)) {
                 $collection = $this->loadCollection();
                 $result = $collection->{$name}(...$arguments);
 
diff --git a/tests/phpstan/phpstan-bootstrap.php b/tests/phpstan/phpstan-bootstrap.php
index 656ca5fd2..b145fa1a0 100644
--- a/tests/phpstan/phpstan-bootstrap.php
+++ b/tests/phpstan/phpstan-bootstrap.php
@@ -4,3 +4,4 @@
  */
 
 define('GRAV_USER_INSTANCE', 'FLEX');
+define('GRAV_REQUEST_TIME', microtime(true));