diff --git a/application/controllers/ConfigController.php b/application/controllers/ConfigController.php
index 8e6febef..8a5e702d 100644
--- a/application/controllers/ConfigController.php
+++ b/application/controllers/ConfigController.php
@@ -370,7 +370,7 @@ class ConfigController extends ActionController
 
         $configs = $db->enumDeployedConfigs();
         foreach (array($leftSum, $rightSum) as $sum) {
-            if (! array_key_exists($sum, $configs)) {
+            if ($sum && ! array_key_exists($sum, $configs)) {
                 $configs[$sum] = substr($sum, 0, 7);
             }
         }
diff --git a/application/controllers/SelfServiceController.php b/application/controllers/SelfServiceController.php
index 6479a298..c3c9bb5a 100644
--- a/application/controllers/SelfServiceController.php
+++ b/application/controllers/SelfServiceController.php
@@ -275,7 +275,7 @@ class SelfServiceController extends ActionController
             // PluginsUrl => framework_plugins_url
         ];
         $username = $settings->get('self-service/icinga_service_user');
-        if ($username !== null && strlen($username) > 0) {
+        if ($username) {
             $params['icinga_service_user'] = $username;
         }
 
@@ -404,7 +404,7 @@ class SelfServiceController extends ActionController
     {
         foreach ($keys as $key) {
             $value = $settings->get("self-service/$key");
-            if (strlen($value)) {
+            if ($value) {
                 $params[$key] = $value;
             }
         }
diff --git a/application/forms/SyncCheckForm.php b/application/forms/SyncCheckForm.php
index 8fb3bd0c..b180d3d3 100644
--- a/application/forms/SyncCheckForm.php
+++ b/application/forms/SyncCheckForm.php
@@ -55,7 +55,7 @@ class SyncCheckForm extends DirectorForm
             } elseif ($sum['modify'] > 1) {
             }
             */
-            $html = '<pre>' . print_r($sum, 1) . '</pre>';
+            $html = '<pre>' . print_r($sum, true) . '</pre>';
 
             $this->addHtml($html);
         } elseif ($this->rule->get('sync_state') === 'in-sync') {
diff --git a/application/views/helpers/FormDataFilter.php b/application/views/helpers/FormDataFilter.php
index f4924d06..a62b906d 100644
--- a/application/views/helpers/FormDataFilter.php
+++ b/application/views/helpers/FormDataFilter.php
@@ -44,14 +44,16 @@ class Zend_View_Helper_FormDataFilter extends Zend_View_Helper_FormElement
     {
         $info = $this->_getInfo($name, $value, $attribs);
         extract($info); // id, name, value, attribs, options, listsep, disable
-        if (array_key_exists('columns', $attribs)) {
-            $this->setColumns($attribs['columns']);
-            unset($attribs['columns']);
-        }
+        if ($attribs) {
+            if (array_key_exists('columns', $attribs)) {
+                $this->setColumns($attribs['columns']);
+                unset($attribs['columns']);
+            }
 
-        if (array_key_exists('suggestionContext', $attribs)) {
-            $this->setSuggestionContext($attribs['suggestionContext']);
-            unset($attribs['suggestionContext']);
+            if (array_key_exists('suggestionContext', $attribs)) {
+                $this->setSuggestionContext($attribs['suggestionContext']);
+                unset($attribs['suggestionContext']);
+            }
         }
 
         // TODO: check for columns in attribs, preserve & remove them from the
diff --git a/library/Director/Cli/ObjectCommand.php b/library/Director/Cli/ObjectCommand.php
index ca68213d..ed99c149 100644
--- a/library/Director/Cli/ObjectCommand.php
+++ b/library/Director/Cli/ObjectCommand.php
@@ -428,7 +428,7 @@ class ObjectCommand extends Command
         }
 
         $stdin = file_get_contents('php://stdin');
-        if (strlen($stdin) === 0) {
+        if (! $stdin) {
             return null;
         }
 
diff --git a/library/Director/Core/CoreApi.php b/library/Director/Core/CoreApi.php
index c1229665..73588c20 100644
--- a/library/Director/Core/CoreApi.php
+++ b/library/Director/Core/CoreApi.php
@@ -569,7 +569,7 @@ constants
             'icon_image_alt'        => 'icon_image_alt',
         ];
 
-        if (version_compare($this->getVersion(), '2.8.0', '>=')) {
+        if (version_compare($this->getVersion() ?? '', '2.8.0', '>=')) {
             $params['flapping_threshold_high'] = 'flapping_threshold_high';
             $params['flapping_threshold_low'] = 'flapping_threshold_low';
         }
diff --git a/library/Director/Core/LegacyDeploymentApi.php b/library/Director/Core/LegacyDeploymentApi.php
index 7287c4a7..0ab77e03 100644
--- a/library/Director/Core/LegacyDeploymentApi.php
+++ b/library/Director/Core/LegacyDeploymentApi.php
@@ -128,6 +128,10 @@ class LegacyDeploymentApi implements DeploymentApiInterface
         if (file_exists($path)) {
             if (is_link($path)) {
                 $linkTarget = readlink($path);
+                if (! $linkTarget) {
+                    throw new IcingaException('Failed to read symlink');
+                }
+
                 $linkTargetDir = dirname($linkTarget);
                 $linkTargetName = basename($linkTarget);
 
@@ -165,7 +169,7 @@ class LegacyDeploymentApi implements DeploymentApiInterface
         $this->assertDeploymentPath();
 
         $dh = @opendir($this->deploymentPath);
-        if ($dh === null) {
+        if ($dh === false) {
             throw new IcingaException('Can not list contents of %s', $this->deploymentPath);
         }
 
@@ -279,7 +283,7 @@ class LegacyDeploymentApi implements DeploymentApiInterface
                 $this->mkdir(dirname($fullPath), true);
 
                 $fh = @fopen($fullPath, 'w');
-                if ($fh === null) {
+                if ($fh === false) {
                     throw new IcingaException('Could not open file "%s" for writing.', $fullPath);
                 }
                 chmod($fullPath, $this->file_mode);
@@ -334,7 +338,7 @@ class LegacyDeploymentApi implements DeploymentApiInterface
     protected function listDirectoryContents($path, $depth = 0)
     {
         $dh = @opendir($path);
-        if ($dh === null) {
+        if ($dh === false) {
             throw new IcingaException('Can not list contents of %s', $path);
         }
 
diff --git a/library/Director/Daemon/BackgroundDaemon.php b/library/Director/Daemon/BackgroundDaemon.php
index 34cc28b7..2d8a29c5 100644
--- a/library/Director/Daemon/BackgroundDaemon.php
+++ b/library/Director/Daemon/BackgroundDaemon.php
@@ -104,7 +104,7 @@ class BackgroundDaemon
             try {
                 $uuid = \bin2hex(Uuid::uuid4()->getBytes());
             } catch (Exception $e) {
-                $uuid = 'deadc0de' . \substr(\md5(\getmypid()), 0, 24);
+                $uuid = 'deadc0de' . substr(md5((string) getmypid()), 0, 24);
             }
         }
         $processDetails = new DaemonProcessDetails($uuid);
diff --git a/library/Director/DirectorObject/ObjectPurgeHelper.php b/library/Director/DirectorObject/ObjectPurgeHelper.php
index a043965d..5e507271 100644
--- a/library/Director/DirectorObject/ObjectPurgeHelper.php
+++ b/library/Director/DirectorObject/ObjectPurgeHelper.php
@@ -44,11 +44,11 @@ class ObjectPurgeHelper
                 // TODO: this is object-specific and to be found in the ::import() function!
                 unset($properties['fields']);
                 $object = $class::fromPlainObject($properties);
-            } elseif (\get_class($object) !== $class) {
+            } elseif (get_class($object) !== $class) {
                 throw new InvalidArgumentException(
                     'Can keep only matching objects, expected "%s", got "%s',
                     $class,
-                    \get_class($keep)
+                    get_class($object)
                 );
             }
             $key = [];
diff --git a/library/Director/Import/ImportSourceRestApi.php b/library/Director/Import/ImportSourceRestApi.php
index dc772e1e..45f7351a 100644
--- a/library/Director/Import/ImportSourceRestApi.php
+++ b/library/Director/Import/ImportSourceRestApi.php
@@ -69,6 +69,7 @@ class ImportSourceRestApi extends ImportSourceHook
         $data = $result;
         foreach ($parts as $part) {
             // un-escape any dots
+            /** @var string $part */
             $part = preg_replace('~\\\\.~', '.', $part);
 
             if (property_exists($data, $part)) {
diff --git a/library/Director/Objects/IcingaCommand.php b/library/Director/Objects/IcingaCommand.php
index 81cac9ed..8c5aed0e 100644
--- a/library/Director/Objects/IcingaCommand.php
+++ b/library/Director/Objects/IcingaCommand.php
@@ -127,10 +127,8 @@ class IcingaCommand extends IcingaObject implements ObjectWithArguments, ExportI
             // return $value;
         }
 
-        if (self::$pluginDir !== null) {
-            if (($pos = strpos($value, self::$pluginDir)) === 0) {
-                $value = substr($value, strlen(self::$pluginDir) + 1);
-            }
+        if (isset($value, self::$pluginDir) && strpos($value, self::$pluginDir) === 0) {
+            $value = substr($value, strlen(self::$pluginDir) + 1);
         }
 
         return $value;
diff --git a/library/Director/PropertyModifier/PropertyModifierGetHostByName.php b/library/Director/PropertyModifier/PropertyModifierGetHostByName.php
index 36884e85..d7921dea 100644
--- a/library/Director/PropertyModifier/PropertyModifierGetHostByName.php
+++ b/library/Director/PropertyModifier/PropertyModifierGetHostByName.php
@@ -34,7 +34,8 @@ class PropertyModifierGetHostByName extends PropertyModifierHook
         }
 
         $host = gethostbyname($value);
-        if (strlen(@inet_pton($host)) !== 4) {
+        $inAddr = inet_pton($host);
+        if (! $inAddr || strlen($inAddr) !== 4) {
             switch ($this->getSetting('on_failure')) {
                 case 'null':
                     return null;
diff --git a/library/Director/ProvidedHook/IcingaDbCubeLinks.php b/library/Director/ProvidedHook/IcingaDbCubeLinks.php
index 234f61fb..f3fe4029 100644
--- a/library/Director/ProvidedHook/IcingaDbCubeLinks.php
+++ b/library/Director/ProvidedHook/IcingaDbCubeLinks.php
@@ -7,6 +7,7 @@ use Icinga\Exception\ProgrammingError;
 use Icinga\Module\Cube\Hook\IcingaDbActionsHook;
 use Icinga\Module\Cube\IcingaDb\IcingaDbCube;
 use Icinga\Module\Cube\IcingaDb\IcingaDbHostStatusCube;
+use ipl\Stdlib\Filter\Condition;
 
 class IcingaDbCubeLinks extends IcingaDbActionsHook
 {
@@ -25,17 +26,19 @@ class IcingaDbCubeLinks extends IcingaDbActionsHook
 
         if ($filterChain->count() === 1) {
             $url = 'director/host/edit?';
-            $params = ['name' => $filterChain->getIterator()->current()->getValue()];
+            /** @var Condition $rule */
+            $rule = $filterChain->getIterator()->current();
+            /** @var string $name */
+            $name = $rule->getValue();
+            $params = ['name' => $name];
 
             $title = t('Modify a host');
-            $description = sprintf(
-                t('This allows you to modify properties for "%s"'),
-                $filterChain->getIterator()->current()->getValue()
-            );
+            $description = sprintf(t('This allows you to modify properties for "%s"'), $name);
         } else {
             $params = null;
 
             $urlFilter = Filter::matchAny();
+            /** @var Condition $filter */
             foreach ($filterChain as $filter) {
                 $urlFilter->addFilter(
                     Filter::matchAny(
diff --git a/library/Director/RestApi/RestApiParams.php b/library/Director/RestApi/RestApiParams.php
index c237ac51..741eeed1 100644
--- a/library/Director/RestApi/RestApiParams.php
+++ b/library/Director/RestApi/RestApiParams.php
@@ -19,8 +19,9 @@ class RestApiParams
             }
             $exporter->enableHostServices();
         }
+        /** @var ?string $properties */
         $properties = $params->shift('properties');
-        if ($properties !== null && strlen($properties)) {
+        if ($properties) {
             $exporter->filterProperties(preg_split('/\s*,\s*/', $properties, -1, PREG_SPLIT_NO_EMPTY));
         }
         $exporter->resolveObjects($resolved);
diff --git a/library/Director/StartupLogRenderer.php b/library/Director/StartupLogRenderer.php
index d9b532a7..9d5810fe 100644
--- a/library/Director/StartupLogRenderer.php
+++ b/library/Director/StartupLogRenderer.php
@@ -33,7 +33,9 @@ class StartupLogRenderer implements ValidHtml
         // len [stage] + 1
         $markReplace = '        ^';
 
-        foreach (preg_split('/\n/', $log) as $line) {
+        /** @var string[] $logLines */
+        $logLines = preg_split('/\n/', $log);
+        foreach ($logLines as $line) {
             if (preg_match('/^\[([\d\s\:\+\-]+)\]\s/', $line, $m)) {
                 $time = $m[1];
                 // TODO: we might use new DateTime($time) and show a special "timeAgo"
diff --git a/library/Director/Web/Controller/ObjectsController.php b/library/Director/Web/Controller/ObjectsController.php
index c45ef021..c4c96c5b 100644
--- a/library/Director/Web/Controller/ObjectsController.php
+++ b/library/Director/Web/Controller/ObjectsController.php
@@ -85,8 +85,9 @@ abstract class ObjectsController extends ActionController
         } elseif ($request->getActionName() === 'applyrules') {
             $table->filterObjectType('apply');
         }
+        /** @var ?string $search */
         $search = $this->params->get('q');
-        if ($search !== null && \strlen($search) > 0) {
+        if ($search) {
             $table->search($search);
         }
 
diff --git a/library/Director/Web/Form/CsrfToken.php b/library/Director/Web/Form/CsrfToken.php
index 24edf88f..f6c29ec9 100644
--- a/library/Director/Web/Form/CsrfToken.php
+++ b/library/Director/Web/Form/CsrfToken.php
@@ -17,7 +17,7 @@ class CsrfToken
             return false;
         }
 
-        list($seed, $token) = explode('|', $elementValue);
+        list($seed, $token) = explode('|', $token);
 
         if (!is_numeric($seed)) {
             return false;
diff --git a/library/Director/Web/Form/DbSelectorForm.php b/library/Director/Web/Form/DbSelectorForm.php
index 52fe5ea3..8b4f4323 100644
--- a/library/Director/Web/Form/DbSelectorForm.php
+++ b/library/Director/Web/Form/DbSelectorForm.php
@@ -69,7 +69,7 @@ class DbSelectorForm extends Form
             $params = [];
         }
 
-        if (array_key_exists($name, $params)) {
+        if (is_array($params) && array_key_exists($name, $params)) {
             return $params[$name];
         }
 
diff --git a/library/Director/Web/Form/DirectorObjectForm.php b/library/Director/Web/Form/DirectorObjectForm.php
index 85562468..abbd4f09 100644
--- a/library/Director/Web/Form/DirectorObjectForm.php
+++ b/library/Director/Web/Form/DirectorObjectForm.php
@@ -791,7 +791,9 @@ abstract class DirectorObjectForm extends DirectorForm
             return;
         }
 
-        $post = $values = $this->getRequest()->getPost();
+        /** @var array $post */
+        $post = $this->getRequest()->getPost();
+        $values = $post;
 
         foreach ($post as $key => $value) {
             if (preg_match('/^(.+?)_(\d+)__(MOVE_DOWN|MOVE_UP|REMOVE)$/', $key, $m)) {
@@ -1519,6 +1521,7 @@ abstract class DirectorObjectForm extends DirectorForm
             return [];
         }
 
+        /** @var int|string $id */
         $id = $object->get('id');
 
         if (array_key_exists($id, $tpl)) {
diff --git a/library/Director/Web/Widget/IcingaObjectInspection.php b/library/Director/Web/Widget/IcingaObjectInspection.php
index 61f35671..d9cf69dd 100644
--- a/library/Director/Web/Widget/IcingaObjectInspection.php
+++ b/library/Director/Web/Widget/IcingaObjectInspection.php
@@ -205,7 +205,7 @@ class IcingaObjectInspection extends BaseHtmlElement
             $this->add(Html::tag('p')->add(Html::sprintf(
                 'The configuration for this object has been rendered by Icinga'
                 . ' Director %s to %s',
-                DateFormatter::timeAgo(strtotime($deployment->start_time, false)),
+                DateFormatter::timeAgo(strtotime($deployment->start_time)),
                 $this->linkToSourceLocation($deployment, $source)
             )));
         }