Don't assume that log_file_permissions exists
diff --git a/system/core/Log.php b/system/core/Log.php
index 57505b5..1dca1bf 100644
--- a/system/core/Log.php
+++ b/system/core/Log.php
@@ -137,7 +137,7 @@
 			$this->_date_fmt = $config['log_date_format'];
 		}
 
-		if (is_int($config['log_file_permissions']))
+		if ( ! empty($config['log_file_permissions']) && is_int($config['log_file_permissions']))
 		{
 			$this->_file_permissions = $config['log_file_permissions'];
 		}