Fix update error in extra_params

app/controllers/v1/collections_controller.rb

@@ -43,7 +43,7 @@ class V1::CollectionsController < ApplicationController
   # PUT/PATCH /v1/users/1.json
   def update
     if @collection.update(collection_params)
-      @collection.add_items(extra_params[:items])
+      @collection.add_items(extra_params[:items]) unless extra_params[:items].is_nil?
       render json: @collection, status: :ok
     else
       render json: @collection.errors, status: :unprocessable_entity