add support for 'undefined' values in json objects

json-box.vue

@@ -35,7 +35,7 @@ export default {
     },
     computed: {
         valueType() {
-            if (this.value === null) {
+            if (this.value === null || this.value === undefined) {
                 return 'Null';
             } else if (Array.isArray(this.value)) {
                 return 'Array';

types/json-null.vue

@@ -1,5 +1,5 @@
 <template>
-    <span class="json-null">null</span>
+    <span class="json-null">{{ jsonValue === null ? 'null' : 'undefined' }}</span>
 </template>
 
 <script>