Proper initialization of out variables everywhere?

[benbovy]

Some output variables in a few processes (like flow receivers, etc.) are not set before the 1st run step.

I'm not sure if it makes sense setting a dummy value for those variables in initialize, as I can't think of a case where those are needed elsewhere during initialization. The only annoying thing is that a KeyError is raised when trying to use it in other process classes at this stage.