diff --git a/system/src/Grav/Common/Assets/Pipeline.php b/system/src/Grav/Common/Assets/Pipeline.php
index 948104ab9..0135e89bd 100644
--- a/system/src/Grav/Common/Assets/Pipeline.php
+++ b/system/src/Grav/Common/Assets/Pipeline.php
@@ -122,7 +122,7 @@ class Pipeline extends PropertyObject
 
         // Compute uid based on assets and timestamp
         $json_assets = json_encode($assets);
-        $uid = md5($json_assets . $this->css_minify . $this->css_rewrite . $group);
+        $uid = md5($json_assets . (int)$this->css_minify . (int)$this->css_rewrite . $group);
         $file = $uid . '.css';
         $relative_path = "{$this->base_url}{$this->assets_url}/{$file}";
 
diff --git a/system/src/Grav/Common/Backup/Backups.php b/system/src/Grav/Common/Backup/Backups.php
index 4680f8546..158e12e2f 100644
--- a/system/src/Grav/Common/Backup/Backups.php
+++ b/system/src/Grav/Common/Backup/Backups.php
@@ -145,7 +145,7 @@ class Backups
     {
         $backups = static::getAvailableBackups();
 
-        return array_sum(array_column($backups, 'size'));
+        return $backups ? array_sum(array_column($backups, 'size')) : 0;
     }
 
     /**
diff --git a/system/src/Grav/Common/Data/Blueprint.php b/system/src/Grav/Common/Data/Blueprint.php
index df434267f..e4f841921 100644
--- a/system/src/Grav/Common/Data/Blueprint.php
+++ b/system/src/Grav/Common/Data/Blueprint.php
@@ -99,7 +99,7 @@ class Blueprint extends BlueprintForm
      */
     public function getDefaultValue(string $name)
     {
-        $path = explode('.', $name) ?: [];
+        $path = explode('.', $name);
         $current = $this->getDefaults();
 
         foreach ($path as $field) {
diff --git a/system/src/Grav/Common/Data/Validation.php b/system/src/Grav/Common/Data/Validation.php
index bfb40578d..9c23f81c2 100644
--- a/system/src/Grav/Common/Data/Validation.php
+++ b/system/src/Grav/Common/Data/Validation.php
@@ -816,7 +816,7 @@ class Validation
     {
         $value = static::filterArray($value, $params, $field);
 
-        return Utils::arrayUnflattenDotNotation($value);
+        return is_array($value) ? Utils::arrayUnflattenDotNotation($value) : null;
     }
 
     /**
diff --git a/system/src/Grav/Common/Filesystem/Folder.php b/system/src/Grav/Common/Filesystem/Folder.php
index ecbc6ceac..6edd8e2e3 100644
--- a/system/src/Grav/Common/Filesystem/Folder.php
+++ b/system/src/Grav/Common/Filesystem/Folder.php
@@ -513,7 +513,7 @@ abstract class Folder
         }
         $directories = glob($directory . '/*', GLOB_ONLYDIR);
 
-        return count($directories);
+        return $directories ? count($directories) : false;
     }
 
     /**
@@ -530,7 +530,8 @@ abstract class Folder
         }
 
         // Go through all items in filesystem and recursively remove everything.
-        $files = array_diff(scandir($folder, SCANDIR_SORT_NONE), array('.', '..'));
+        $files = scandir($folder, SCANDIR_SORT_NONE);
+        $files = $files ? array_diff($files, ['.', '..']) : [];
         foreach ($files as $file) {
             $path = "{$folder}/{$file}";
             is_dir($path) ? self::doDelete($path) : @unlink($path);
diff --git a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
index 25d8672c0..4974a3acf 100644
--- a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
@@ -131,7 +131,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     {
         $key = $this->isAllowedElement($element) ? $this->getCurrentKey($element) : null;
 
-        if (!$key || !isset($this->entries[$key])) {
+        if (null !== $key || !isset($this->entries[$key])) {
             return false;
         }
 
@@ -148,7 +148,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
-        return $this->containsKey($offset);
+        return $offset !== null ? $this->containsKey($offset) : false;
     }
 
     /**
@@ -159,7 +159,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
-        return $this->get($offset);
+        return $offset !== null ? $this->get($offset) : null;
     }
 
     /**
@@ -172,9 +172,9 @@ abstract class AbstractIndexCollection implements CollectionInterface
     {
         if (null === $offset) {
             $this->add($value);
+        } else {
+            $this->set($offset, $value);
         }
-
-        $this->set($offset, $value);
     }
 
     /**
@@ -185,7 +185,9 @@ abstract class AbstractIndexCollection implements CollectionInterface
     #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
-        $this->remove($offset);
+        if ($offset !== null) {
+            $this->remove($offset);
+        }
     }
 
     /**
diff --git a/system/src/Grav/Framework/File/AbstractFile.php b/system/src/Grav/Framework/File/AbstractFile.php
index 0c78dd303..af9209c68 100644
--- a/system/src/Grav/Framework/File/AbstractFile.php
+++ b/system/src/Grav/Framework/File/AbstractFile.php
@@ -191,8 +191,9 @@ class AbstractFile implements FileInterface
             $this->handle = @fopen($this->filepath, 'cb+') ?: null;
             if (!$this->handle) {
                 $error = error_get_last();
+                $message = $error['message'] ?? 'Unknown error';
 
-                throw new RuntimeException("Opening file for writing failed on error {$error['message']}");
+                throw new RuntimeException("Opening file for writing failed on error {$message}");
             }
         }
 
diff --git a/system/src/Grav/Framework/File/Formatter/YamlFormatter.php b/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
index 32d4d296a..3909f6e85 100644
--- a/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
@@ -107,7 +107,9 @@ class YamlFormatter extends AbstractFormatter
             $saved = @ini_get('yaml.decode_php');
             @ini_set('yaml.decode_php', '0');
             $decoded = @yaml_parse($data);
-            @ini_set('yaml.decode_php', $saved);
+            if ($saved !== false) {
+                @ini_set('yaml.decode_php', $saved);
+            }
 
             if ($decoded !== false) {
                 return (array) $decoded;