this saves us saying a load of someAttribute IS NOTHING

Example

DECLARE Person HAS
  Name IS A STRING
  BirthDate IS A MAYBE Date
  Nationality IS A MAYBE Country

Previous to this patch, we would have had to say:

`John Doe` MEANS Person WITH
  Name IS "John Doe"
  BirthDate IS NOTHING
  Nationality IS NOTHING

After this patch, we can say:

`John Doe` MEANS Person WITH
  Name IS "John Doe"

And the MAYBE attributes get auto-set to NOTHING.

Note that this only works for the WITH / IS form of instantiation – the OF syntax doesn't benefit from this.