Failed to Compare two elments in a array.

最近遇到一个奇怪的问题，是第三方控件Third Party的问题，

Failed to Compare two elments in a array.

System.InvalidOperationException: Failed to compare two elements in the array. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Infragistics.Win.ValueListItemsCollection.ValueListComparer.Compare(Object o1, Object o2)
   at System.Array.BinarySearch(Array array, Int32 index, Int32 length, Object value, IComparer comparer)
   --- End of inner exception stack trace ---
   at System.Array.BinarySearch(Array array, Int32 index, Int32 length, Object value, IComparer comparer)
   at System.Collections.ArrayList.BinarySearch(Int32 index, Int32 count, Object value, IComparer comparer)
   at System.Collections.ArrayList.BinarySearch(Object value, IComparer comparer)
   at Infragistics.Win.ValueListItemsCollection.IndexOf(Object valueListItem)
   at Infragistics.Win.ValueList.set_SelectedItem(Object value)
   at K2.Mod.Core.DocumentOrganiseEdit.PopulateDropDown() in D:\K2Development\K2\K2.Mod.Core\Document Organiser\DocumentOrganiseEdit.cs:line 431
   at K2.Mod.Core.DocumentOrganiseEdit.InitializeData() in D:\K2Development\K2\K2.Mod.Core\Document Organiser\DocumentOrganiseEdit.cs:line 345
   at K2.Mod.Core.DocumentOrganiseEdit.DocumentOrganiseEdit_Shown(Object sender, EventArgs e) in D:\K2Development\K2\K2.Mod.Core\Document Organiser\DocumentOrganiseEdit.cs:line 80

网上搜了下是因为没有实现IComparable接口。