DateTimePicker selectedDate throws exception when selected date is null

Hi, Initially am initializing a CustomValue to null for showing Watermark then it is throwing exception i.e String was not recognized as a valid date(converter failed to convert value)

<DateTimePicker Height="25"
   Width="200"
   Focusable="False"
   controls:TextBoxHelper.AutoWatermark="True"
   SelectedDate="{Binding CustomValue, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
   Margin="5,5"
   HorizontalAlignment="Stretch"/>

How to handle these exception or initially how to show watermark ?

Thanks, Raghav

[punker76]

@Raghava56 It’s a nullable DateTime: public Nullable<DateTime> SelectedDate { get; set; }

[Raghava56]

@punker76 Then why it is throwing exception. if SelectedDate is a nullable data type then it should accept null value.