update null

git-svn-id: http://10.4.3.168:50001/svn/Furnace@53 dbcde07d-dcf5-c148-8a84-ac3097b7778e

FrameworkLocal/UIClient/CenterViews/DataLogs/ProcessHistory/ProcessHistoryTwoViewModel.cs

@@ -102,7 +102,11 @@ namespace MECF.Framework.UI.Client.CenterViews.DataLogs.ProcessHistory
             this.view.wfTimeTo.Content = this.SearchEndTime;
 
             QueryLots(new object());
-            ProcessHistoryLots.FirstOrDefault().IsChecked = true;
+
+            if (ProcessHistoryLots!=null&& ProcessHistoryLots.FirstOrDefault() != null)
+            {
+                ProcessHistoryLots.FirstOrDefault().IsChecked = true;
+            }
         }
 
         void InitTime()