Why is ConversionRate a Parameter and not a Function?

[Anaphory]

Building an example, I just noticed that

contacTrees/src/contactrees/model/ConversionRate.java

Line 12 in ab1df01

public class ConversionRate extends RealParameter {

It seems that ConversionRate has no state (or ignores its state), so why is it not a Function instead? Are there BEAST2 objects that we want to feed a ConversionRate into which expect a RealParameter even though a Function should suffice? It wouldn't be the first time.

[Anaphory]

Talking to @NicoNeureiter we suspect that either operators need StateNode inputs (and RealParameter was the easiest way to work around that), or that the forward simulation needs this to be a sub-class of Parameter.