DerbyJS: Don't error on undefined list, ensure num active count is reactive fn.

labs/architecture-examples/derbyjs/src/todos/index.coffee

@@ -4,9 +4,12 @@ derby = require 'derby'
 derby.use(require '../../ui')
 
 view.fn 'noItems',
-	get: (list) -> !list.length
+	get: (list) -> !list.length unless list is undefined
 	set: ->
 
+view.fn 'oneItem',
+	get: (list) -> list.length == 1 unless list is undefined
+
 # Redirect the visitor to a random todo list
 get '/', (page) ->
 	page.redirect '/' + parseInt(Math.random() * 1e9).toString(36)

labs/architecture-examples/derbyjs/views/todos/index.html

@@ -40,7 +40,7 @@
 
 <todoFooter:>
 	<footer id="footer" class="{#unless _list.all}empty-list{/}">
-	<span id="todo-count"><strong>{_list.active.length}</strong> item{#unless equal(_list.active.length, 1)}s{/} left</span>
+	<span id="todo-count"><strong>{_list.active.length}</strong> item{#unless oneItem(_list.active)}s{/} left</span>
 		<ul id="filters">
 			<li class="all">
 				<a href="/{{_groupName}}" class="{#if equal(_filter, 'all')}selected{/}">All</a>