Allow "Spent Fuel" conditions on Trains

[burgersnfries]

While playing mods that have fuel with a spent result that I can load into a locomotive as its fuel, I'm often left with trains leaving the station with contents in their "spent" slot. This is a problem, as once the "spent" slot is full, the trains behave as though they are out of fuel, as they can no longer burn fuel. I'd like to be able to check the contents of the spent slot as part of train conditions so I can ensure that they are empty before they leave stations.

[Amarula]

I'm doing a Nullius run right now and I agree it would be nice to have something like this for trains. We can read all the contents of buildings including these kind of by products, why not trains?
As a work around maybe you could use inactivity?