support NULL for date index defaultvalue

Global_Indexer/ClassControls.vb

@@ -363,7 +363,7 @@ Public Class ClassControls
     End Sub
 
 
-    Public Function AddDateTimePicker(indexname As String, y As Integer, DataType As String) As DevExpress.XtraEditors.DateEdit
+    Public Function AddDateTimePicker(indexname As String, y As Integer, DataType As String, Vorgabe As String) As DevExpress.XtraEditors.DateEdit
         Dim oPicker As New DevExpress.XtraEditors.DateEdit With {
             .Name = "dtp" & indexname,
             .Size = New Size(260, 27),
@@ -373,6 +373,11 @@ Public Class ClassControls
                 .IndexType = DataType
             }
         }
+
+        If Vorgabe = "NULL" Then
+            oPicker.EditValue = Nothing
+        End If
+
         oPicker.Properties.AppearanceFocused.BackColor = Color.Lime
 
         Return oPicker