fix bug in units

pkg/ui/frontend/src/components/AddItemForm.vue

@@ -124,7 +124,7 @@ export default {
     name: "",
     description: "",
     size: null,
-    unit: "",
+    unit: null,
     units: [
       { value: 0, text: "Teaspoon" },
       { value: 1, text: "Tablespoon" },
@@ -191,7 +191,7 @@ export default {
         name: this.name,
         description: this.description,
         size: this.size,
-        unit: this.unit.id,
+        unit: this.unit,
         location: {"id": this.location},
         barcode: this.barcode,
       };