System.NullReferenceException was caught
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=DevExpress.Diagram.v15.2.Core
  StackTrace:
       at DevExpress.Diagram.Core.PropertyDescriptorHelper.GetValue(Object x, String path)
       at DevExpress.Diagram.Core.KeyParentModeDataProvider.GetNotNullKey(Object node, String member)
       at DevExpress.Diagram.Core.KeyParentModeDataProvider.<>c__DisplayClass6.<.ctor>b__0(Object node)
       at System.Linq.Lookup`2.Create[TSource](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
       at System.Linq.GroupedEnumerable`3.GetEnumerator()
       at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
       at DevExpress.Diagram.Core.KeyParentModeDataProvider..ctor(IEnumerable itemsSource, String keyMember, String parentMember)
       at DevExpress.Diagram.Core.OrgChartController.CreateProvider()
       at DevExpress.Diagram.Core.OrgChartController.<PopulateDiagram>b__0()
       at DevExpress.Diagram.Core.DiagramExtensions.LoadDocument(IDiagramControl diagram, Action loadAction)
       at DevExpress.Diagram.Core.OrgChartController.PopulateDiagram()
       at DevExpress.Diagram.Core.OrgChartController.OnItemsSourceChanged()
       at <My Application Path>.OrgChartBehavior`1.OnItemsSourceChanged()
       at <My Application Path>.OrgChartBehavior`1.set_ItemsSource(IEnumerable value)
       at <My Application Path>.FrmDiagramViewer.Init(IList`1& data, Boolean isRevert)
  InnerException: