Today's faulty, pain-in-the-ass code.

gistfile1.xml

        <xctk:EditorDefinitionCollection x:Key="StandardPropertyEditors" x:Shared="False">
            <xctk:EditorTemplateDefinition TargetProperties="{arkane:Nullable TypeName=system:Boolean}" >
                <xctk:EditorTemplateDefinition.EditingTemplate>
                    <DataTemplate>
                        <CheckBox IsChecked="{Binding Value}" IsThreeState="True" />
                    </DataTemplate>
                </xctk:EditorTemplateDefinition.EditingTemplate>
            </xctk:EditorTemplateDefinition>
            <xctk:EditorTemplateDefinition TargetProperties="{arkane:Nullable system:DateTime}">
                <xctk:EditorTemplateDefinition.EditingTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Value}" />
                    </DataTemplate>
                </xctk:EditorTemplateDefinition.EditingTemplate>
            </xctk:EditorTemplateDefinition>
            <xctk:EditorTemplateDefinition TargetProperties="{x:Type database:User}">
                <xctk:EditorTemplateDefinition.EditingTemplate>
                    <DataTemplate>
                        <controls1:NullItemSelectorAdapter
                                        ItemsSource="{Binding Mode=OneWay, Source={StaticResource UserLookup}}">
                            <ComboBox SelectedItem="{Binding Value, UpdateSourceTrigger=PropertyChanged, TargetNullValue=(None)}" ItemContainerStyleSelector="{StaticResource InactiveUserStyleSelector}" />
                        </controls1:NullItemSelectorAdapter>
                    </DataTemplate>
                </xctk:EditorTemplateDefinition.EditingTemplate>
            </xctk:EditorTemplateDefinition>
            <xctk:EditorTemplateDefinition TargetProperties="{x:Type database:EnumerationValue}">
                <xctk:EditorTemplateDefinition.EditingTemplate>
                    <DataTemplate>
                        <controls:EnumerationFilterAdapter
                                        ItemsSource="{Binding Mode=OneWay, Source={StaticResource EnumerationValueLookup}}"
                                        DatabasePropertyName="{Binding DisplayName, Mode=OneWay}">
                            <ComboBox
                                            SelectedItem="{Binding Value, UpdateSourceTrigger=PropertyChanged, TargetNullValue=(None)}" />
                        </controls:EnumerationFilterAdapter>
                    </DataTemplate>
                </xctk:EditorTemplateDefinition.EditingTemplate>
            </xctk:EditorTemplateDefinition>
        </xctk:EditorDefinitionCollection>