Default mac to NULL.

bootstrap.sql

@@ -40,7 +40,7 @@ CREATE TABLE `SWITCHES` (
 CREATE TABLE `DEVICE_MAP` (
     serial_number varchar(64) NOT NULL,
     pid varchar(64) NOT NULL,
-    mac varchar(17) NOT NULL,
+    mac varchar(17) DEFAULT NULL, /*Note: This is not used now. */
     max_ports int NOT NULL,
     assigned_switch varchar(64),
     checked_out tinyint(1) DEFAULT '0',