diff --git a/application/clicommands/MigrateCommand.php b/application/clicommands/MigrateCommand.php
index c5eb8fbf..b5accb8c 100644
--- a/application/clicommands/MigrateCommand.php
+++ b/application/clicommands/MigrateCommand.php
@@ -787,7 +787,7 @@ class MigrateCommand extends Command
         return $config;
     }
 
-    private function createBackupIni(string $path, Config $config = null): void
+    private function createBackupIni(string $path, ?Config $config = null): void
     {
         $counter = 0;
         while (true) {
diff --git a/application/forms/RedisConfigForm.php b/application/forms/RedisConfigForm.php
index cfaa0750..ef911c1d 100644
--- a/application/forms/RedisConfigForm.php
+++ b/application/forms/RedisConfigForm.php
@@ -676,13 +676,13 @@ class RedisConfigForm extends ConfigForm
      * Wraps the given IPL validator class into a callback validator
      * for usage as the only validator of the element given by name.
      *
-     * @param   string  $cls        IPL validator class FQN
-     * @param   string  $element    Form element name
-     * @param   Closure $additionalValidator
+     * @param string $cls IPL validator class FQN
+     * @param string $element Form element name
+     * @param ?Closure $additionalValidator
      *
-     * @return  array               Callback validator
+     * @return array Callback validator
      */
-    private function wrapIplValidator(string $cls, string $element, Closure $additionalValidator = null): array
+    private function wrapIplValidator(string $cls, string $element, ?Closure $additionalValidator = null): array
     {
         return [
             'Callback',
diff --git a/library/Icingadb/Command/Object/ProcessCheckResultCommand.php b/library/Icingadb/Command/Object/ProcessCheckResultCommand.php
index 875a5f18..d63912c1 100644
--- a/library/Icingadb/Command/Object/ProcessCheckResultCommand.php
+++ b/library/Icingadb/Command/Object/ProcessCheckResultCommand.php
@@ -118,11 +118,11 @@ class ProcessCheckResultCommand extends ObjectsCommand
     /**
      * Set the performance data of the host or service check result
      *
-     * @param   string|null $performanceData
+     * @param ?string $performanceData
      *
-     * @return  $this
+     * @return $this
      */
-    public function setPerformanceData(string $performanceData = null): self
+    public function setPerformanceData(?string $performanceData = null): self
     {
         $this->performanceData = $performanceData;
 
diff --git a/library/Icingadb/Command/Transport/ApiCommandTransport.php b/library/Icingadb/Command/Transport/ApiCommandTransport.php
index 3857d865..1d8f497a 100644
--- a/library/Icingadb/Command/Transport/ApiCommandTransport.php
+++ b/library/Icingadb/Command/Transport/ApiCommandTransport.php
@@ -301,13 +301,13 @@ class ApiCommandTransport implements CommandTransportInterface
      * Send the Icinga command over the Icinga 2 API
      *
      * @param IcingaCommand|IcingaApiCommand $command
-     * @param int|null $now
+     * @param ?int $now
      *
      * @throws CommandTransportException
      *
      * @return mixed
      */
-    public function send(IcingaCommand|IcingaApiCommand $command, int $now = null)
+    public function send(IcingaCommand|IcingaApiCommand $command, ?int $now = null)
     {
         if ($command instanceof IcingaCommand) {
             $command = $this->renderer->render($command);
diff --git a/library/Icingadb/Command/Transport/CommandTransport.php b/library/Icingadb/Command/Transport/CommandTransport.php
index 75cad032..03358a1e 100644
--- a/library/Icingadb/Command/Transport/CommandTransport.php
+++ b/library/Icingadb/Command/Transport/CommandTransport.php
@@ -94,14 +94,14 @@ class CommandTransport implements CommandTransportInterface
      *
      * This will try one configured transport after another until the command has been successfully sent.
      *
-     * @param   IcingaCommand   $command    The command to send
-     * @param   int|null        $now        Timestamp of the command or null for now
+     * @param IcingaCommand $command The command to send
+     * @param ?int $now Timestamp of the command or null for now
      *
-     * @throws  CommandTransportException   If sending the Icinga command failed
+     * @return mixed
      *
-     * @return  mixed
+     * @throws CommandTransportException If sending the Icinga command failed
      */
-    public function send(IcingaCommand $command, int $now = null)
+    public function send(IcingaCommand $command, ?int $now = null)
     {
         $errors = [];
         $results = [];
diff --git a/library/Icingadb/Command/Transport/CommandTransportInterface.php b/library/Icingadb/Command/Transport/CommandTransportInterface.php
index 48423461..ac5dc642 100644
--- a/library/Icingadb/Command/Transport/CommandTransportInterface.php
+++ b/library/Icingadb/Command/Transport/CommandTransportInterface.php
@@ -15,10 +15,10 @@ interface CommandTransportInterface
     /**
      * Send an Icinga command over the Icinga command transport
      *
-     * @param   IcingaCommand   $command    The command to send
-     * @param   int|null        $now        Timestamp of the command or null for now
+     * @param IcingaCommand $command The command to send
+     * @param ?int $now Timestamp of the command or null for now
      *
-     * @throws  CommandTransportException If sending the Icinga command failed
+     * @throws CommandTransportException If sending the Icinga command failed
      */
-    public function send(IcingaCommand $command, int $now = null);
+    public function send(IcingaCommand $command, ?int $now = null);
 }
diff --git a/library/Icingadb/Common/HostStates.php b/library/Icingadb/Common/HostStates.php
index 06b6dad5..cf2840c5 100644
--- a/library/Icingadb/Common/HostStates.php
+++ b/library/Icingadb/Common/HostStates.php
@@ -47,13 +47,13 @@ class HostStates
     /**
      * Get the textual representation of the passed host state
      *
-     * @param int|null $state
+     * @param ?int $state
      *
      * @return string
      *
      * @throws \InvalidArgumentException If the given host state is invalid, i.e. not known
      */
-    public static function text(int $state = null): string
+    public static function text(?int $state = null): string
     {
         switch (true) {
             case $state === self::UP:
@@ -78,13 +78,13 @@ class HostStates
     /**
      * Get the translated textual representation of the passed host state
      *
-     * @param int|null $state
+     * @param ?int $state
      *
      * @return string
      *
      * @throws \InvalidArgumentException If the given host state is invalid, i.e. not known
      */
-    public static function translated(int $state = null): string
+    public static function translated(?int $state = null): string
     {
         switch (true) {
             case $state === self::UP:
diff --git a/library/Icingadb/Common/IcingaRedis.php b/library/Icingadb/Common/IcingaRedis.php
index 231ecc01..3e9a1293 100644
--- a/library/Icingadb/Common/IcingaRedis.php
+++ b/library/Icingadb/Common/IcingaRedis.php
@@ -173,11 +173,11 @@ class IcingaRedis
     /**
      * Get the last icinga heartbeat from redis
      *
-     * @param Redis|null $redis
+     * @param ?Redis $redis
      *
      * @return float|int|null
      */
-    public static function getLastIcingaHeartbeat(Redis $redis = null)
+    public static function getLastIcingaHeartbeat(?Redis $redis = null)
     {
         if ($redis === null) {
             $redis = Backend::getRedis()->getConnection();
@@ -201,12 +201,12 @@ class IcingaRedis
     /**
      * Get the primary redis instance
      *
-     * @param Config|null $moduleConfig
-     * @param Config|null $redisConfig
+     * @param ?Config $moduleConfig
+     * @param ?Config $redisConfig
      *
      * @return Redis
      */
-    public static function getPrimaryRedis(Config $moduleConfig = null, Config $redisConfig = null): Redis
+    public static function getPrimaryRedis(?Config $moduleConfig = null, ?Config $redisConfig = null): Redis
     {
         if ($moduleConfig === null) {
             $moduleConfig = Config::module('icingadb');
@@ -235,12 +235,12 @@ class IcingaRedis
     /**
      * Get the secondary redis instance if exists
      *
-     * @param Config|null $moduleConfig
-     * @param Config|null $redisConfig
+     * @param ?Config $moduleConfig
+     * @param ?Config $redisConfig
      *
      * @return ?Redis
      */
-    public static function getSecondaryRedis(Config $moduleConfig = null, Config $redisConfig = null)
+    public static function getSecondaryRedis(?Config $moduleConfig = null, ?Config $redisConfig = null)
     {
         if ($moduleConfig === null) {
             $moduleConfig = Config::module('icingadb');
diff --git a/library/Icingadb/Common/ServiceStates.php b/library/Icingadb/Common/ServiceStates.php
index 68aea14c..5dd6b114 100644
--- a/library/Icingadb/Common/ServiceStates.php
+++ b/library/Icingadb/Common/ServiceStates.php
@@ -57,13 +57,13 @@ class ServiceStates
     /**
      * Get the textual representation of the passed service state
      *
-     * @param int|null $state
+     * @param ?int $state
      *
      * @return string
      *
      * @throws \InvalidArgumentException If the given service state is invalid, i.e. not known
      */
-    public static function text(int $state = null): string
+    public static function text(?int $state = null): string
     {
         switch (true) {
             case $state === self::OK:
@@ -94,13 +94,13 @@ class ServiceStates
     /**
      * Get the translated textual representation of the passed service state
      *
-     * @param int|null $state
+     * @param ?int $state
      *
      * @return string
      *
      * @throws \InvalidArgumentException If the given service state is invalid, i.e. not known
      */
-    public static function translated(int $state = null): string
+    public static function translated(?int $state = null): string
     {
         switch (true) {
             case $state === self::OK:
diff --git a/library/Icingadb/Common/StateBadges.php b/library/Icingadb/Common/StateBadges.php
index eaa246e5..f30226f6 100644
--- a/library/Icingadb/Common/StateBadges.php
+++ b/library/Icingadb/Common/StateBadges.php
@@ -118,7 +118,7 @@ abstract class StateBadges extends BaseHtmlElement
      *
      * @return Link
      */
-    protected function createLink($content, Filter\Rule $filter = null): Link
+    protected function createLink($content, ?Filter\Rule $filter = null): Link
     {
         $url = clone $this->getUrl();
 
diff --git a/library/Icingadb/Compat/UrlMigrator.php b/library/Icingadb/Compat/UrlMigrator.php
index 8d5321c2..62e9ac5c 100644
--- a/library/Icingadb/Compat/UrlMigrator.php
+++ b/library/Icingadb/Compat/UrlMigrator.php
@@ -84,7 +84,7 @@ class UrlMigrator
         return $url;
     }
 
-    public static function transformParams(Url $url, string $transformerName = null): array
+    public static function transformParams(Url $url, ?string $transformerName = null): array
     {
         $transformer = new self();
 
@@ -153,11 +153,11 @@ class UrlMigrator
      * Transform the given legacy filter
      *
      * @param Filter\Rule $filter
-     * @param string|null $queryTransformer
+     * @param ?string $queryTransformer
      *
      * @return Filter\Rule|false
      */
-    public static function transformFilter(Filter\Rule $filter, string $queryTransformer = null)
+    public static function transformFilter(Filter\Rule $filter, ?string $queryTransformer = null)
     {
         $transformer = new self();
 
diff --git a/library/Icingadb/Data/PivotTable.php b/library/Icingadb/Data/PivotTable.php
index 2e75a5c8..4613c355 100644
--- a/library/Icingadb/Data/PivotTable.php
+++ b/library/Icingadb/Data/PivotTable.php
@@ -115,11 +115,11 @@ class PivotTable
     /**
      * Set the filter to apply on the query for the x-axis
      *
-     * @param   Filter\Rule  $filter
+     * @param ?Filter\Rule $filter
      *
-     * @return  $this
+     * @return $this
      */
-    public function setXAxisFilter(Filter\Rule $filter = null): self
+    public function setXAxisFilter(?Filter\Rule $filter = null): self
     {
         $this->xAxisFilter = $filter;
         return  $this;
@@ -128,11 +128,11 @@ class PivotTable
     /**
      * Set the filter to apply on the query for the y-axis
      *
-     * @param   Filter\Rule  $filter
+     * @param ?Filter\Rule $filter
      *
-     * @return  $this
+     * @return $this
      */
-    public function setYAxisFilter(Filter\Rule $filter = null): self
+    public function setYAxisFilter(?Filter\Rule $filter = null): self
     {
         $this->yAxisFilter = $filter;
         return  $this;
@@ -203,13 +203,13 @@ class PivotTable
     /**
      * Return the value for the given request parameter
      *
-     * @param   string  $axis       The axis for which to return the parameter ('x' or 'y')
-     * @param   string  $param      The parameter name to return
-     * @param   int     $default    The default value to return
+     * @param string $axis The axis for which to return the parameter ('x' or 'y')
+     * @param string $param The parameter name to return
+     * @param ?int $default The default value to return
      *
-     * @return  int
+     * @return int
      */
-    protected function getPaginationParameter(string $axis, string $param, int $default = null): int
+    protected function getPaginationParameter(string $axis, string $param, ?int $default = null): int
     {
         /** @var Web $app */
         $app = Icinga::app();
@@ -326,12 +326,12 @@ class PivotTable
      *
      * $limit and $page are taken from the current request if not given.
      *
-     * @param   int     $limit  The maximum amount of entries to fetch
-     * @param   int     $page   The page to set as current one
+     * @param ?int $limit The maximum amount of entries to fetch
+     * @param ?int $page The page to set as current one
      *
-     * @return  Paginatable
+     * @return Paginatable
      */
-    public function paginateXAxis(int $limit = null, int $page = null): Paginatable
+    public function paginateXAxis(?int $limit = null, ?int $page = null): Paginatable
     {
         if ($limit === null || $page === null) {
             if ($limit === null) {
@@ -358,12 +358,12 @@ class PivotTable
      *
      * $limit and $page are taken from the current request if not given.
      *
-     * @param int $limit The maximum amount of entries to fetch
-     * @param int $page The page to set as current one
+     * @param ?int $limit The maximum amount of entries to fetch
+     * @param ?int $page The page to set as current one
      *
-     * @return  Paginatable
+     * @return Paginatable
      */
-    public function paginateYAxis(int $limit = null, int $page = null): Paginatable
+    public function paginateYAxis(?int $limit = null, ?int $page = null): Paginatable
     {
         if ($limit === null || $page === null) {
             if ($limit === null) {
diff --git a/library/Icingadb/Hook/Common/TotalSlaReportUtils.php b/library/Icingadb/Hook/Common/TotalSlaReportUtils.php
index 687c0c0f..5ae5dcb1 100644
--- a/library/Icingadb/Hook/Common/TotalSlaReportUtils.php
+++ b/library/Icingadb/Hook/Common/TotalSlaReportUtils.php
@@ -14,7 +14,7 @@ use function ipl\I18n\t;
 
 trait TotalSlaReportUtils
 {
-    public function getHtml(Timerange $timerange, array $config = null)
+    public function getHtml(Timerange $timerange, ?array $config = null)
     {
         $data = $this->getData($timerange, $config);
         $count = $data->count();
diff --git a/library/Icingadb/Model/UnreachableParent.php b/library/Icingadb/Model/UnreachableParent.php
index acb9dc37..0d634f49 100644
--- a/library/Icingadb/Model/UnreachableParent.php
+++ b/library/Icingadb/Model/UnreachableParent.php
@@ -86,7 +86,7 @@ class UnreachableParent extends DependencyNode
         ]));
     }
 
-    public static function on(Connection $db, Model $root = null): Query
+    public static function on(Connection $db, ?Model $root = null): Query
     {
         if ($root === null) {
             throw new InvalidArgumentException('Root node must not be null');
diff --git a/library/Icingadb/ProvidedHook/Reporting/HostSlaReport.php b/library/Icingadb/ProvidedHook/Reporting/HostSlaReport.php
index d12d646a..e975545c 100644
--- a/library/Icingadb/ProvidedHook/Reporting/HostSlaReport.php
+++ b/library/Icingadb/ProvidedHook/Reporting/HostSlaReport.php
@@ -45,7 +45,7 @@ class HostSlaReport extends SlaReport
             ->setValues([(float) $row->sla]);
     }
 
-    protected function fetchSla(Timerange $timerange, Rule $filter = null)
+    protected function fetchSla(Timerange $timerange, ?Rule $filter = null)
     {
         $sla = Host::on($this->getDb())
             ->columns([
diff --git a/library/Icingadb/ProvidedHook/Reporting/ServiceSlaReport.php b/library/Icingadb/ProvidedHook/Reporting/ServiceSlaReport.php
index 4b118050..fb281d5c 100644
--- a/library/Icingadb/ProvidedHook/Reporting/ServiceSlaReport.php
+++ b/library/Icingadb/ProvidedHook/Reporting/ServiceSlaReport.php
@@ -45,7 +45,7 @@ class ServiceSlaReport extends SlaReport
             ->setValues([(float) $row->sla]);
     }
 
-    protected function fetchSla(Timerange $timerange, Rule $filter = null)
+    protected function fetchSla(Timerange $timerange, ?Rule $filter = null)
     {
         $sla = Service::on($this->getDb())
             ->columns([
diff --git a/library/Icingadb/ProvidedHook/Reporting/SlaReport.php b/library/Icingadb/ProvidedHook/Reporting/SlaReport.php
index 0d4cae36..6e3bb81d 100644
--- a/library/Icingadb/ProvidedHook/Reporting/SlaReport.php
+++ b/library/Icingadb/ProvidedHook/Reporting/SlaReport.php
@@ -56,13 +56,13 @@ abstract class SlaReport extends ReportHook
      * Fetch SLA according to specified time range and filter
      *
      * @param Timerange $timerange
-     * @param Rule|null $filter
+     * @param ?Rule $filter
      *
      * @return iterable
      */
-    abstract protected function fetchSla(Timerange $timerange, Rule $filter = null);
+    abstract protected function fetchSla(Timerange $timerange, ?Rule $filter = null);
 
-    protected function fetchReportData(Timerange $timerange, array $config = null)
+    protected function fetchReportData(Timerange $timerange, ?array $config = null)
     {
         $rd = $this->createReportData();
         $rows = [];
@@ -214,12 +214,12 @@ abstract class SlaReport extends ReportHook
         ]);
     }
 
-    public function getData(Timerange $timerange, array $config = null)
+    public function getData(Timerange $timerange, ?array $config = null)
     {
         return $this->fetchReportData($timerange, $config);
     }
 
-    public function getHtml(Timerange $timerange, array $config = null)
+    public function getHtml(Timerange $timerange, ?array $config = null)
     {
         $data = $this->getData($timerange, $config);
 
diff --git a/library/Icingadb/ProvidedHook/X509/Sni.php b/library/Icingadb/ProvidedHook/X509/Sni.php
index eab1946c..5de953cc 100644
--- a/library/Icingadb/ProvidedHook/X509/Sni.php
+++ b/library/Icingadb/ProvidedHook/X509/Sni.php
@@ -21,7 +21,7 @@ class Sni extends SniHook
     /**
      * @inheritDoc
      */
-    public function getHosts(Filter $filter = null): Generator
+    public function getHosts(?Filter $filter = null): Generator
     {
         $this->getDb()->ping();
 
diff --git a/library/Icingadb/Util/PerfDataSet.php b/library/Icingadb/Util/PerfDataSet.php
index 19c4b9af..f4303ecc 100644
--- a/library/Icingadb/Util/PerfDataSet.php
+++ b/library/Icingadb/Util/PerfDataSet.php
@@ -135,11 +135,11 @@ class PerfDataSet implements IteratorAggregate
      * Return all characters between the current parser position and the given character
      *
      * @param string $stopChar The character on which to stop
-     * @param string $backtrackOn The character on which to backtrack
+     * @param ?string $backtrackOn The character on which to backtrack
      *
      * @return string
      */
-    protected function readUntil(string $stopChar, string $backtrackOn = null): string
+    protected function readUntil(string $stopChar, ?string $backtrackOn = null): string
     {
         $start = $this->parserPos;
         $breakCharEncounteredAt = null;
diff --git a/library/Icingadb/Web/Controller.php b/library/Icingadb/Web/Controller.php
index 45429e2d..ea045aa7 100644
--- a/library/Icingadb/Web/Controller.php
+++ b/library/Icingadb/Web/Controller.php
@@ -319,11 +319,11 @@ class Controller extends CompatController
     /**
      * Require permission to access the given route
      *
-     * @param string $name If NULL, the current controller name is used
+     * @param ?string $name If NULL, the current controller name is used
      *
      * @throws SecurityException
      */
-    public function assertRouteAccess(string $name = null)
+    public function assertRouteAccess(?string $name = null)
     {
         if (! $name) {
             $name = $this->getRequest()->getControllerName();
@@ -451,7 +451,7 @@ class Controller extends CompatController
         return parent::addContent($content);
     }
 
-    public function filter(Query $query, Filter\Rule $filter = null): self
+    public function filter(Query $query, ?Filter\Rule $filter = null): self
     {
         if ($this->format !== 'sql' || $this->hasPermission('config/authentication/roles/show')) {
             $this->applyRestrictions($query);
diff --git a/library/Icingadb/Web/Navigation/Renderer/ProblemsBadge.php b/library/Icingadb/Web/Navigation/Renderer/ProblemsBadge.php
index 85a8b01c..db1fc13e 100644
--- a/library/Icingadb/Web/Navigation/Renderer/ProblemsBadge.php
+++ b/library/Icingadb/Web/Navigation/Renderer/ProblemsBadge.php
@@ -115,7 +115,7 @@ abstract class ProblemsBadge extends NavigationItemRenderer
         return $this->title;
     }
 
-    public function render(NavigationItem $item = null): string
+    public function render(?NavigationItem $item = null): string
     {
         if ($item === null) {
             $item = $this->getItem();
diff --git a/library/Icingadb/Widget/Detail/CustomVarTable.php b/library/Icingadb/Widget/Detail/CustomVarTable.php
index e2265e0e..67359e09 100644
--- a/library/Icingadb/Widget/Detail/CustomVarTable.php
+++ b/library/Icingadb/Widget/Detail/CustomVarTable.php
@@ -52,7 +52,7 @@ class CustomVarTable extends BaseHtmlElement
      * @param iterable $data
      * @param ?Model $object
      */
-    public function __construct($data, Model $object = null)
+    public function __construct($data, ?Model $object = null)
     {
         $this->data = $data;
         $this->object = $object;
diff --git a/library/Icingadb/Widget/ShowMore.php b/library/Icingadb/Widget/ShowMore.php
index 4558c50d..faaf6f50 100644
--- a/library/Icingadb/Widget/ShowMore.php
+++ b/library/Icingadb/Widget/ShowMore.php
@@ -28,7 +28,7 @@ class ShowMore extends BaseHtmlElement
     /** @var ?string */
     protected $label;
 
-    public function __construct(ResultSet $resultSet, Url $url, string $label = null)
+    public function __construct(ResultSet $resultSet, Url $url, ?string $label = null)
     {
         $this->label = $label;
         $this->resultSet = $resultSet;
diff --git a/test/php/library/Icingadb/Common/StateBadgesTest.php b/test/php/library/Icingadb/Common/StateBadgesTest.php
index 45c32911..4aad786c 100644
--- a/test/php/library/Icingadb/Common/StateBadgesTest.php
+++ b/test/php/library/Icingadb/Common/StateBadgesTest.php
@@ -84,7 +84,7 @@ class StateBadgesTest extends TestCase
                 return 0;
             }
 
-            public function generateLink($content, Filter\Rule $filter = null): Link
+            public function generateLink($content, ?Filter\Rule $filter = null): Link
             {
                 return parent::createLink($content, $filter);
             }