public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
{
if (destinationType == null)
{
throw new ArgumentNullException(nameof(destinationType));
}
if (destinationType == typeof(string))
{
if (value == null)
{
return NullString;
}
else if (value == DBNull.Value)
{
return DbNullString;
}
}
return base.ConvertTo(context, culture, value, destinationType);
}