I'm passing a List of Custom Objects to my Custom Exception Class and need to display all the objects in the message. How can I do this?

```
public class MissingUnitSNSException : Exception
{
    public MissingUnitSNSException()
    {

    }

    public MissingUnitSNSException(List<UnitViewModel> missingsns)
        : base(String.Format("Serial Numbers not found: {0}", missingsns))
    {

    }
}

```

The error tells me the type of object, but I need the serial number attribute that's tied to each object in the list.