I have the case where a subsystem of my model can be commented out. In that case, the outports connected to the outputs of that subsystems will give a zero when the simulation is run. In my case, I don't want anything at all, since afterwards I'm checking if a given signal exists or not, and since a 0 was given, the signal seems to exist, but it should not.
If I simply use Ctrl+Shift+X (Comment Out) on the outport, I get the warning dialog "Commenting out of the following block(s) is not supported: my_model/my_outport".
Running on Matlab 2017b.