Additional error check

Author: Jake Ginnivan

src/TestStack.White/UIItems/MenuItems/Menus.cs

@@ -12,10 +12,11 @@ namespace TestStack.White.UIItems.MenuItems
 {
     public class Menus : UIItemList<Menu>
     {
-        private static readonly DictionaryMappedItemFactory Factory = new DictionaryMappedItemFactory();
+        static readonly DictionaryMappedItemFactory Factory = new DictionaryMappedItemFactory();
 
         public Menus(AutomationElement parent, ActionListener actionListener)
         {
+            if (parent == null) throw new ArgumentNullException("parent", "You must specify a parent automation id when creating a menu");
             AutomationSearchCondition condition = AutomationSearchCondition.ByControlType(ControlType.MenuItem);
             var finder = new AutomationElementFinder(parent);
             finder = PerformanceHackAsPopupMenuForWin32AppComesOnDesktop(finder, parent);

src/TestStack.White/UIItems/MenuItems/PopUpMenu.cs

@@ -6,28 +6,26 @@ namespace TestStack.White.UIItems.MenuItems
 {
     public class PopUpMenu : UIItem
     {
-        private readonly Menus topLevelMenus;
         protected PopUpMenu() {}
 
         public PopUpMenu(AutomationElement automationElement, ActionListener actionListener) : base(automationElement, actionListener)
         {
             this.actionListener = actionListener;
-            topLevelMenus = new Menus(automationElement, actionListener);
         }
 
         public virtual Menus Items
         {
-            get { return topLevelMenus; }
+            get { return new Menus(automationElement, actionListener); }
         }
 
         public virtual Menu Item(params string[] text)
         {
-            return topLevelMenus.Find(text);
+            return Items.Find(text);
         }
 
         public virtual Menu ItemBy(params SearchCriteria[] path)
         {
-            return topLevelMenus.Find(path);
+            return Items.Find(path);
         }
     }
 }