Revert/optimize some changes from ed944a3c70a0bad158cd5a6ca5ce1f2e717aff5d
diff --git a/system/core/CodeIgniter.php b/system/core/CodeIgniter.php
index 182f17a..b3e984d 100755
--- a/system/core/CodeIgniter.php
+++ b/system/core/CodeIgniter.php
@@ -94,7 +94,7 @@
  * Note: Since the config file data is cached it doesn't
  * hurt to load it here.
  */
-	if (isset($assign_to_config['subclass_prefix']) && $assign_to_config['subclass_prefix'] !== '')
+	if ( ! empty($assign_to_config['subclass_prefix']))
 	{
 		get_config(array('subclass_prefix' => $assign_to_config['subclass_prefix']));
 	}