Make serial and serial.port optional.

lib/util/settings.js

@@ -126,10 +126,9 @@ const schema = {
         serial: {
             type: 'object',
             properties: {
-                port: {type: ['string', 'null']},
+                port: {type: ['string']},
                 disable_led: {type: 'boolean'},
             },
-            required: ['port'],
         },
         ban: {type: 'array', items: {type: 'string'}},
         whitelist: {type: 'array', items: {type: 'string'}},
@@ -230,7 +229,7 @@ const schema = {
             },
         },
     },
-    required: ['homeassistant', 'permit_join', 'mqtt', 'serial'],
+    required: ['homeassistant', 'permit_join', 'mqtt'],
 };