GettextFormatConverter returns empty string when binding value is null

[Jogge]

I'm trying to bind to this property with the GettextFormatConverter and the value of Date is null:

public Class SomeClass {
    public DateTime? Date { get; set; } = null
}

<TextBlock Text="{Binding SomeClass.Date, Mode=OneWay, Converter={wpf:GettextFormatConverter Date: {0}}}" />

Expected result: Date:

Result: