How do I pass or access the default value for a custom my token?

I've constructed a custom my token that access a custom object.  But that object may not exist.  I'd like to just display a default that can be passed in just like all of the regular tokens, but nothing seems to work.  This is what I have in the email:

{{my.DisplayTitle:default=This is Default Title}}

However, the default here is never displayed.  Is there someway to access this in the token script or pass back an "undefined" to trigger the default?  The default seems to work fine with the standard tokens, but there doesn't seem to be a way to write your own token and show a default if nothing is defined.

Thanks!