Minor fixes
diff --git a/system/core/Output.php b/system/core/Output.php
index df9ef07..238d223 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -243,7 +243,7 @@
 		}
 
 		$header = 'Content-Type: '.$mime_type
-			.(empty($charset) ? NULL : '; charset='.$charset);
+			.(empty($charset) ? '' : '; charset='.$charset);
 
 		$this->headers[] = array($header, TRUE);
 		return $this;