NullReferenceException in "Datepicker"

Hi

 I'm using build 20080822 of the WPF propertygrid.  I have the following code

Xaml

<window x:class="PropertyGridSample.Window1" 
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
              xmlns:ms="http://namespaces.mindscape.co.nz/wpf" title="Window1" height="300" width="300">
	<grid>
         <ms:propertygrid selectedobject="{Binding}"/>
       </grid>
</window>

C#

namespace PropertyGridSample {
  public partial class Window1 {
    public Window1() {
        InitializeComponent();
        DataContext = new Person();
    }
  }
  public class Person {
    public DateTime BirthDay { get; set; }
  }
}

This shows a PropertyGrid with a single property "BirthDay", when I click the dropdown in the "DatePicker" the a NullReferenceException is thrown with stack trace found below.

 Do I need to add something to prevent the datepicker to work, or is this a bug the in the build?

 System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=IsDropDownOpen; DataItem='DropDown' (Name=''); target element is 'DropDownToggleButton' (Name=''); target property is 'IsChecked' (type 'Nullable`1') XamlParseException:'System.Windows.Markup.XamlParseException:  Cannot find type 'Mindscape.WpfPropertyGrid.DayTemplateSelector'. The assembly used when compiling might be different than that used when loading and the type is missing.  Error in markup file 'Mindscape.WpfPropertyGrid;component/Themes/Calendar.Generic.xaml'. ---> System.ApplicationException: Cannot find type 'Mindscape.WpfPropertyGrid.DayTemplateSelector'. The assembly used when compiling might be different than that used when loading and the type is missing.
   at System.Windows.Markup.BamlMapTable.ThrowException(String id, String parameter)
   at System.Windows.Markup.BamlMapTable.GetTypeFromId(Int16 id)
   at System.Windows.Markup.BamlRecordReader.GetElementAndFlags(BamlElementStartRecord bamlElementStartRecord, Object& element, ReaderFlags& flags, Type& delayCreatedType, Int16& delayCreatedTypeId)
   at System.Windows.Markup.BamlRecordReader.BaseReadElementStartRecord(BamlElementStartRecord bamlElementRecord)
   at System.Windows.Markup.BamlRecordReader.ReadElementStartRecord(BamlElementStartRecord bamlElementRecord)
   at System.Windows.Markup.BamlRecordReader.ReadRecord(BamlRecord bamlRecord)

This was a bug resulting from an overenthusiastic obfuscator.  I have now fixed it and the fix will be available in builds numbered 20080827 and above, available after about 1800 GMT.

In the meantime, the bug only manifests if you have a DateTime in January 0001 or December 9999.  So you can get around it by specifying a BirthDay value that is not in either of those two months.  We would generally advise using a more appropriate default for DateTime properties than DateTime.MinValue anyway.

Apologies for the inconvenience and thanks for reporting the problem.