Just updated my game to 1.2.0, got the following error message:

Failed to load mods: Error while loading entity prototype "derpy-cluster-artillery-ammo-projectileFromRenairTransportationPrimed" (stream): Value must be a dictionary in property tree at ROOT.stream.derpy-cluster-artillery-ammo-projectileFromRenairTransportationPrimed.initial_action[0]

Among my mods is the Light Artillery mod, which disabling lets me load the latest version.

Maybe it's set up differently than what my code scans for for projectile effects. Is it this mod you're talking about?
https://mods.factorio.com/mod/lightArtillery

I seem to have a similar error from rampant arsenal for incendiary artillery ammunition since the last update. I'm assuming they're related

Looks like the problem was I didn't consider a projectile could have more than 1 effect. Should be good now though, I could load light artillery and rampant without crash