Prevent access to uninitialized members or static variables

Author: Cyperghost

wcfsetup/install/files/lib/system/cache/eager/AbstractEagerCache.class.php

@@ -53,7 +53,11 @@ private function getCacheKey(): string
             );
 
             $parameters = [];
-            foreach ($reflection->getProperties() as $property) {
+            foreach ($reflection->getProperties(\ReflectionProperty::IS_READONLY) as $property) {
+                if (!$property->isInitialized($this)) {
+                    continue;
+                }
+
                 $value = $property->getValue($this);
                 if ($value === null) {
                     continue;