bugfix

assets/javascripts/wizard/components/wizard-field-category.js.es6

@@ -3,27 +3,30 @@ import Category from 'discourse/models/category';
 
 export default Ember.Component.extend({
   didInsertElement() {
-    const value = this.get('field.value');
+    const property = this.field.property || 'id';
+    const value = this.field.value;
+    
     if (value) {
-      const property = this.get('field.property') || 'id';
-      const categories = [...value].map(v => {
-        return property === 'id' ?
-               Category.findById(v) :
-               Category.findBySlug(v);
-      });
-      this.set('categories', categories);
+      this.set('categories', [...value].reduce((result, v) => {
+        let val = property === 'id' ? Category.findById(v) : Category.findBySlug(v);
+        if (val) result.push(val);
+        return result;
+      }, []));
     }
   },
-
+  
   @observes('categories')
   setValue() {
-    const categories = this.get('categories');
-    if (categories.length) {
-      const property = this.get('field.property') || 'id';
-      let value = categories.length === 1 ?
-                  categories[0][property] :
-                  categories.map(c => c[property]);
-      this.set('field.value', value);
+    const categories = (this.categories || []).filter(c => !!c);
+    const property = this.field.property || 'id';
+    
+    if (categories.length) {            
+      this.set('field.value', categories.reduce((result, c) => {
+        if (c && c[property]) {
+          result.push(c[property])
+        }
+        return result;
+      }, []));
     }
   }
 });