`PointMass` inputs do not carry scale factors.

[bartvanerp]

When directly plugging in numbers or fixed values into the model specification, this will send out messages as expected, but these messages do not include scale factors. For example:

y ~ Switch(z, (0, 1))

causes issues later on, because the message corresponding to 0 and 1 have a unknown log-scaling (which should be 0).