Forge now throws a fatal error if a mod is missing the license field in the mods.toml. This is the same as shedaniel/cloth-config#60
Here's some interesting info: https://forums.minecraftforge.net/topic/89070-forge-server-wont-start-with-mods-in-fodler/
The exact error is: [java.lang.ThreadGroup:uncaughtException:1052]: net.minecraftforge.fml.loading.moddiscovery.InvalidModFileException: Missing License, please supply a license. (light-overlay-5.4.1.jar)

Forge seems to require it in the 1.16.2 version but was already displaying warnings in older versions. If you don't want to give a license, you could still fill the field with a placeholder string. (Although it's strongly recommended you choose a license since the code is already public)

Light Overlay is licensed under Apache 2.0. I just don't want to recompile for 1.16.1 to simply add a license field.

No I'm just saying you can add the license field and then it's included the next time you release it to enable the next release to run on 1.16.2.

isn't this just required in the 1.16.2 version?