Index: src/wp-admin/options.php
===================================================================
--- src/wp-admin/options.php	(revision 43686)
+++ src/wp-admin/options.php	(working copy)
@@ -272,7 +272,7 @@
 			}
 
 			$option = trim( $option );
-			$value  = null;
+			$value  = '';
 			if ( isset( $_POST[ $option ] ) ) {
 				$value = $_POST[ $option ];
 				if ( ! is_array( $value ) ) {