Bugfix/Properly handle passed null to $className parameter (#2)

Author: segoddnja

.idea/php.xml

@@ -497,7 +497,7 @@ protected function create($className)
      */
     protected function exists($className)
     {
-        return class_exists($className) || $this->container->bound($className);
+        return !!$className && class_exists($className) || $this->container->bound($className);
     }
 
 }