diff --git a/src/Contao/Callback/Callbacks.php b/src/Contao/Callback/Callbacks.php
index ae2c8ef3..115aef6e 100644
--- a/src/Contao/Callback/Callbacks.php
+++ b/src/Contao/Callback/Callbacks.php
@@ -132,6 +132,9 @@ protected static function evaluateCallback($callback)
             if ($serviceCallback[0] !== $callback[0]) {
                 return $serviceCallback;
             }
+            if (!\class_exists($callback[0])) {
+                return $callback;
+            }
 
             $class = new ReflectionClass($callback[0]);
 
diff --git a/src/Contao/Compatibility/DcCompat.php b/src/Contao/Compatibility/DcCompat.php
index 6d1fefa8..f4a9e883 100644
--- a/src/Contao/Compatibility/DcCompat.php
+++ b/src/Contao/Compatibility/DcCompat.php
@@ -22,30 +22,35 @@
 
 namespace ContaoCommunityAlliance\DcGeneral\Contao\Compatibility;
 
+use ContaoCommunityAlliance\DcGeneral\Data\DataProviderInterface;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelId;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelInterface;
+use ContaoCommunityAlliance\DcGeneral\DataDefinition\ContainerInterface;
 use ContaoCommunityAlliance\DcGeneral\DC\General;
 use ContaoCommunityAlliance\DcGeneral\EnvironmentInterface;
 use ContaoCommunityAlliance\DcGeneral\Exception\DcGeneralException;
 use ContaoCommunityAlliance\DcGeneral\Exception\DcGeneralRuntimeException;
 use ContaoCommunityAlliance\DcGeneral\Factory\Event\PopulateEnvironmentEvent;
+use ContaoCommunityAlliance\DcGeneral\InputProviderInterface;
 
 /**
  * Small compatibility layer for callbacks, that expect a "full-featured" DC instance.
+ *
+ * @psalm-suppress PropertyNotSetInConstructor
  */
 class DcCompat extends General
 {
     /**
      * The current model.
      *
-     * @var ModelInterface
+     * @var ModelInterface|null
      */
     protected $model;
 
     /**
      * Name of the property currently working on.
      *
-     * @var string
+     * @var string|null
      */
     protected $propertyName;
 
@@ -53,7 +58,7 @@ class DcCompat extends General
      * Create a new instance.
      *
      * @param EnvironmentInterface $environment  The Dc instance to use for delegating.
-     * @param ModelInterface       $model        The model within scope (optional).
+     * @param ModelInterface|null  $model        The model within scope (optional).
      * @param string|null          $propertyName The name of the property within scope (optional).
      */
     public function __construct(EnvironmentInterface $environment, ModelInterface $model = null, $propertyName = null)
@@ -71,7 +76,7 @@ public function __construct(EnvironmentInterface $environment, ModelInterface $m
     /**
      * Retrieve the current model.
      *
-     * @return ModelInterface
+     * @return ModelInterface|null
      */
     public function getModel()
     {
@@ -81,7 +86,7 @@ public function getModel()
     /**
      * Retrieve the current property.
      *
-     * @return string
+     * @return string|null
      */
     public function getPropertyName()
     {
@@ -89,9 +94,13 @@ public function getPropertyName()
     }
 
     /**
-     * {@inheritdoc}
+     * Internal use only.
      *
      * @throws DcGeneralException This method is for internal use only.
+     *
+     * @return never
+     *
+     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
      */
     public function handlePopulateEnvironment(PopulateEnvironmentEvent $event)
     {
@@ -105,7 +114,7 @@ public function handlePopulateEnvironment(PopulateEnvironmentEvent $event)
      *
      * @throws DcGeneralException This method is for internal use only.
      */
-    protected function getTablenameCallback($strTable)
+    protected function getTablenameCallback($tableName)
     {
         throw new DcGeneralException(
             __CLASS__ . '::getTablenameCallback() is internal use only and must not be called'
@@ -134,12 +143,18 @@ public function __get($name)
         switch ($name) {
             case 'id':
                 if (null !== $this->getModel()) {
-                    return $this->getModel()->getId();
+                    $model = $this->getModel();
+                    assert($model instanceof ModelInterface);
+                    return $model->getId();
                 }
 
-                $environment    = $this->getEnvironment();
+                $environment = $this->getEnvironment();
+
                 $dataDefinition = $environment->getDataDefinition();
-                $inputProvider  = $environment->getInputProvider();
+                assert($dataDefinition instanceof ContainerInterface);
+
+                $inputProvider = $environment->getInputProvider();
+                assert($inputProvider instanceof InputProviderInterface);
 
                 $idParameter = $inputProvider->hasParameter('id') ? 'id' : 'pid';
                 if (!$inputProvider->hasParameter($idParameter)) {
@@ -168,7 +183,10 @@ public function __get($name)
 
             case 'parentTable':
                 if ($this->getEnvironment()->getParentDataDefinition()) {
-                    return $this->getEnvironment()->getParentDataDefinition()->getName();
+                    $container = $this->getEnvironment()->getParentDataDefinition();
+                    assert($container instanceof ContainerInterface);
+
+                    return $container->getName();
                 }
                 return null;
 
@@ -182,11 +200,16 @@ public function __get($name)
                 throw new DcGeneralRuntimeException('The magic property $dc->createNewVersion is not supported yet!');
 
             case 'table':
-                return $this->getEnvironment()->getDataProvider()->getEmptyModel()->getProviderName();
+                $dataProvider = $this->getEnvironment()->getDataProvider();
+                assert($dataProvider instanceof DataProviderInterface);
+
+                return $dataProvider->getEmptyModel()->getProviderName();
 
             case 'value':
                 if ($this->propertyName && $this->getModel()) {
-                    return $this->getModel()->getProperty($this->propertyName);
+                    $model = $this->getModel();
+                    assert($model instanceof ModelInterface);
+                    return $model->getProperty($this->propertyName);
                 }
                 return null;
 
@@ -200,6 +223,7 @@ public function __get($name)
                 throw new DcGeneralRuntimeException('The magic property $dc->palette is not supported yet!');
 
             case 'activeRecord':
+                assert($this->model instanceof ModelInterface);
                 return new ActiveRecord($this->model);
 
             default:
diff --git a/src/Contao/Dca/Builder/Legacy/LegacyDcaDataDefinitionBuilder.php b/src/Contao/Dca/Builder/Legacy/LegacyDcaDataDefinitionBuilder.php
index 9c35455e..ba96bb0a 100644
--- a/src/Contao/Dca/Builder/Legacy/LegacyDcaDataDefinitionBuilder.php
+++ b/src/Contao/Dca/Builder/Legacy/LegacyDcaDataDefinitionBuilder.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2022 Contao Community Alliance.
+ * (c) 2013-2023 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -17,7 +17,7 @@
  * @author     Stefan Heimes <stefan_heimes@hotmail.com>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
- * @copyright  2013-2022 Contao Community Alliance.
+ * @copyright  2013-2023 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -162,7 +162,7 @@ public function build(ContainerInterface $container, BuildDataDefinitionEvent $e
      * Register the callback handlers for the given legacy callbacks.
      *
      * @param EventDispatcherInterface $dispatcher The event dispatcher.
-     * @param array                    $callbacks  The callbacks to be handled.
+     * @param list<callable>|callable  $callbacks  The callbacks to be handled.
      * @param string                   $eventName  The event to be registered to.
      * @param array                    $arguments  The arguments to pass to the constructor.
      * @param class-string             $listener   The listener class to use.
@@ -175,14 +175,11 @@ public function build(ContainerInterface $container, BuildDataDefinitionEvent $e
      */
     protected function parseCallback($dispatcher, $callbacks, $eventName, $arguments, $listener)
     {
-        if (!(is_array($callbacks) || is_callable($callbacks))) {
-            return;
-        }
-
         // If only one callback given, ensure the loop below handles it correctly.
-        if (is_array($callbacks) && (2 === count($callbacks)) && !is_array($callbacks[0])) {
+        if (is_array($callbacks) && (2 === count($callbacks)) && !is_array($callbacks[0] ?? [])) {
             $callbacks = [$callbacks];
         }
+
         foreach ((array) $callbacks as $callback) {
             if ($this->isCallbackBlacklisted($callback, $listener)) {
                 continue;
@@ -198,17 +195,17 @@ protected function parseCallback($dispatcher, $callbacks, $eventName, $arguments
     /**
      * Check if callback is blacklisted.
      *
-     * @param mixed  $callback The callback.
-     * @param string $listener The listener class.
+     * @param mixed        $callback The callback.
+     * @param class-string $listener The listener class.
      *
      * @return bool
      */
-    private function isCallbackBlacklisted($callback, $listener)
+    private function isCallbackBlacklisted(mixed $callback, string $listener): bool
     {
         return ((ContainerOnLoadCallbackListener::class === $listener)
                 && is_array($callback)
                 && ('checkPermission' === $callback[1])
-                && (0 === strpos($callback[0], 'tl_')));
+                && (str_starts_with($callback[0], 'tl_')));
     }
 
     /**
diff --git a/src/Contao/View/Contao2BackendView/ActionHandler/MultipleHandler/OverrideAllHandler.php b/src/Contao/View/Contao2BackendView/ActionHandler/MultipleHandler/OverrideAllHandler.php
index b70cced3..ac676e98 100644
--- a/src/Contao/View/Contao2BackendView/ActionHandler/MultipleHandler/OverrideAllHandler.php
+++ b/src/Contao/View/Contao2BackendView/ActionHandler/MultipleHandler/OverrideAllHandler.php
@@ -350,7 +350,11 @@ private function renderFieldSets(
     private function getModelFromWidget(Widget $widget): ModelInterface
     {
         if ($widget->dataContainer instanceof DcCompat) {
-            return $widget->dataContainer->getModel();
+            $model = $widget->dataContainer->getModel();
+            if (null === $model) {
+                throw new \InvalidArgumentException('Datacontainer does not hold a model.');
+            }
+            return $model;
         }
         if ($widget instanceof AbstractWidget) {
             return $widget->getModel();
diff --git a/src/Contao/View/Contao2BackendView/EditMask.php b/src/Contao/View/Contao2BackendView/EditMask.php
index 64cadd2e..f409436c 100644
--- a/src/Contao/View/Contao2BackendView/EditMask.php
+++ b/src/Contao/View/Contao2BackendView/EditMask.php
@@ -1021,17 +1021,10 @@ public function execute()
     private function executeMultiLanguage(ContaoBackendViewTemplate $template)
     {
         $dataProvider = $this->getEnvironment()->getDataProvider($this->model->getProviderName());
-        assert($dataProvider instanceof DataProviderInterface);
-
         if (
-            \in_array(
-                MultiLanguageDataProviderInterface::class,
-                \class_implements($dataProvider)
-            )
+            $dataProvider instanceof MultiLanguageDataProviderInterface
+            && null !== $dataProvider->getLanguages($this->model->getId())
         ) {
-            /** @var MultiLanguageDataProviderInterface $dataProvider */
-            $dataProvider = $this->getEnvironment()->getDataProvider();
-
             $locales = System::getContainer()->get('contao.intl.locales');
             assert($locales instanceof Locales);
 
@@ -1043,10 +1036,8 @@ private function executeMultiLanguage(ContaoBackendViewTemplate $template)
             $translator = $this->environment->getTranslator();
             assert($translator instanceof TranslatorInterface);
 
-            $template->set(
-                'languages',
-                $controller->getSupportedLanguages($this->model->getId())
-            )
+            $template
+                ->set('languages', $controller->getSupportedLanguages($this->model->getId()))
                 ->set('language', $dataProvider->getCurrentLanguage())
                 ->set('languageSubmit', $translator->translate('MSC.showSelected'))
                 ->set('languageHeadline', $languages[$dataProvider->getCurrentLanguage()] ?? '');
diff --git a/src/Contao/View/Contao2BackendView/Subscriber/GetGroupHeaderSubscriber.php b/src/Contao/View/Contao2BackendView/Subscriber/GetGroupHeaderSubscriber.php
index b3282c20..af9edb7b 100644
--- a/src/Contao/View/Contao2BackendView/Subscriber/GetGroupHeaderSubscriber.php
+++ b/src/Contao/View/Contao2BackendView/Subscriber/GetGroupHeaderSubscriber.php
@@ -53,14 +53,14 @@ class GetGroupHeaderSubscriber
      *
      * @var EventDispatcherInterface
      */
-    private $dispatcher;
+    private EventDispatcherInterface $dispatcher;
 
     /**
      * The translator.
      *
      * @var TranslatorInterface
      */
-    private $translator;
+    private TranslatorInterface $translator;
 
     /**
      * Create a new instance.
@@ -136,6 +136,7 @@ protected function formatGroupHeader(
         if (isset($evaluation['multiple']) && !$evaluation['multiple'] && ('checkbox' === $property->getWidgetType())) {
             return $this->formatCheckboxOptionLabel($model->getProperty($property->getName()));
         }
+
         if (GroupAndSortingInformationInterface::GROUP_NONE !== $groupingMode) {
             return $this->formatByGroupingMode($groupingMode, $groupingLength, $environment, $property, $model);
         }
@@ -240,9 +241,9 @@ private function formatByCharGrouping($value, $groupingLength)
      *
      * @param int $value The value.
      *
-     * @return string|null
+     * @return string
      */
-    private function formatByDayGrouping(int $value): ?string
+    private function formatByDayGrouping(int $value): string
     {
         $value = $this->getTimestamp($value);
 
@@ -263,13 +264,14 @@ private function formatByDayGrouping(int $value): ?string
      *
      * @return string
      */
-    private function formatByWeekGrouping(int $value): ?string
+    private function formatByWeekGrouping(int $value): string
     {
         $value = $this->getTimestamp($value);
 
         if (0 === $value) {
             return '-';
         }
+
         $event = new ParseDateEvent($value, $this->translator->translate('MSC.week_format'));
         $this->dispatcher->dispatch($event, ContaoEvents::DATE_PARSE);
 
@@ -281,15 +283,16 @@ private function formatByWeekGrouping(int $value): ?string
      *
      * @param int $value The value.
      *
-     * @return string|null
+     * @return string
      */
-    private function formatByMonthGrouping(int $value): ?string
+    private function formatByMonthGrouping(int $value): string
     {
         $value = $this->getTimestamp($value);
 
         if (0 === $value) {
             return '-';
         }
+
         $event = new ParseDateEvent($value, 'F Y');
         $this->dispatcher->dispatch($event, ContaoEvents::DATE_PARSE);
 
@@ -317,11 +320,11 @@ private function formatByYearGrouping($value)
     /**
      * Make sure a timestamp is returned.
      *
-     * @param int|\DateTime $value The given date.
+     * @param \DateTime|int $value The given date.
      *
      * @return int
      */
-    private function getTimestamp($value)
+    private function getTimestamp(\DateTime|int $value): int
     {
         return ($value instanceof \DateTime) ? $value->getTimestamp() : $value;
     }
diff --git a/src/Contao/View/Contao2BackendView/Widget/AbstractWidget.php b/src/Contao/View/Contao2BackendView/Widget/AbstractWidget.php
index f47c3e0e..fb462e22 100644
--- a/src/Contao/View/Contao2BackendView/Widget/AbstractWidget.php
+++ b/src/Contao/View/Contao2BackendView/Widget/AbstractWidget.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2023 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -14,7 +14,8 @@
  * @author     David Molineus <david.molineus@netzmacht.de>
  * @author     Christian Schiffler <c.schiffler@cyberspectrum.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     Ingolf Steinhardt <info@e-spin.de>
+ * @copyright  2013-2023 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -91,6 +92,9 @@ public function getEnvironment()
     public function getModel()
     {
         assert($this->dataContainer instanceof DcCompat);
-        return $this->dataContainer->getModel();
+        $model = $this->dataContainer->getModel();
+        assert($model instanceof ModelInterface);
+
+        return $model;
     }
 }
diff --git a/src/DC/General.php b/src/DC/General.php
index d2f2f504..6d3c8672 100644
--- a/src/DC/General.php
+++ b/src/DC/General.php
@@ -50,6 +50,8 @@
 /**
  * This class is only present so Contao can instantiate a backend properly as it needs a \DataContainer descendant.
  *
+ * @psalm-suppress PropertyNotSetInConstructor
+ *
  * @SuppressWarnings(PHPMD.TooManyPublicMethods)
  * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
  */
@@ -58,7 +60,7 @@ class General extends DataContainer implements DataContainerInterface
     /**
      * The environment attached to this DC.
      *
-     * @var EnvironmentInterface
+     * @var EnvironmentInterface|null
      */
     protected $objEnvironment;
 
@@ -95,6 +97,7 @@ public function __construct($tableName, array $module = [], CacheInterface $cach
             }
             $this->objEnvironment = $event->getEnvironment();
         }, $this, $this);
+        assert($fetcher instanceof \Closure);
         $dispatcher->addListener(PopulateEnvironmentEvent::NAME, $fetcher, 4800);
 
         (new DcGeneralFactory($cache))
@@ -121,9 +124,12 @@ public function __construct($tableName, array $module = [], CacheInterface $cach
      *
      * @return EventDispatcherInterface
      */
-    private function getEventDispatcher()
+    private function getEventDispatcher(): EventDispatcherInterface
     {
-        return System::getContainer()->get('event_dispatcher');
+        $dispatcher = System::getContainer()->get('event_dispatcher');
+        assert($dispatcher instanceof EventDispatcherInterface);
+
+        return $dispatcher;
     }
 
     /**
@@ -131,9 +137,12 @@ private function getEventDispatcher()
      *
      * @return TranslatorInterface
      */
-    private function getTranslator()
+    private function getTranslator(): TranslatorInterface
     {
-        return System::getContainer()->get('cca.translator.contao_translator');
+        $translator = System::getContainer()->get('cca.translator.contao_translator');
+        assert($translator instanceof TranslatorInterface);
+
+        return $translator;
     }
 
     /**
@@ -240,7 +249,7 @@ public function getName()
      */
     public function getEnvironment()
     {
-        if (!$this->objEnvironment) {
+        if (null === $this->objEnvironment) {
             throw new DcGeneralRuntimeException('No Environment set.');
         }
 
@@ -254,7 +263,10 @@ public function getEnvironment()
      */
     public function getViewHandler()
     {
-        return $this->getEnvironment()->getView();
+        $view = $this->getEnvironment()->getView();
+        assert($view instanceof ViewInterface);
+
+        return $view;
     }
 
     /**
@@ -264,7 +276,10 @@ public function getViewHandler()
      */
     public function getControllerHandler()
     {
-        return $this->getEnvironment()->getController();
+        $controller = $this->getEnvironment()->getController();
+        assert($controller instanceof ControllerInterface);
+
+        return $controller;
     }
 
     /**
@@ -416,7 +431,7 @@ public function undo()
      *
      * @deprecated Only here as requirement of \DataContainer
      *
-     * @return void
+     * @return never
      *
      * @throws DcGeneralRuntimeException Throws exception because method is not supported.
      */
diff --git a/src/DataContainerInterface.php b/src/DataContainerInterface.php
index ea9fec8d..2b7c84c0 100644
--- a/src/DataContainerInterface.php
+++ b/src/DataContainerInterface.php
@@ -21,9 +21,15 @@
 
 namespace ContaoCommunityAlliance\DcGeneral;
 
+use Contao\EditableDataContainerInterface;
+use Contao\ListableDataContainerInterface;
+
 /**
  * This interface describes an object providing access to an environment.
  */
-interface DataContainerInterface extends \editable, \listable, EnvironmentAwareInterface
+interface DataContainerInterface extends
+    EditableDataContainerInterface,
+    ListableDataContainerInterface,
+    EnvironmentAwareInterface
 {
 }
diff --git a/src/Panel/DefaultLimitElement.php b/src/Panel/DefaultLimitElement.php
index 77e50b44..c518df7f 100644
--- a/src/Panel/DefaultLimitElement.php
+++ b/src/Panel/DefaultLimitElement.php
@@ -199,7 +199,7 @@ private function defineOffsetAndAmountOption(int &$offset, int &$amount): void
             return;
         }
 
-        if ($input->hasValue('tl_limit') && $this->getPanel()?->getContainer()->updateValues()) {
+        if ($input->hasValue('tl_limit') && $this->getPanel()->getContainer()->updateValues()) {
             $limit = $input->getValue('tl_limit');
             if ('all' === $limit) {
                 $offset = 0;