I find that returning nil is generally far easier to work with, The savings comes in something like this from an effected mod: for _, neighbour in pairs(entity.neighbours) do... If entity.neighbours is an empty collection, then the for loop just doesn't do anything with no check for nil or empty re...

Regardless of what the docs say, returning an empty collection generally allows for more concise client code than returning nil. This change has also broken at least two mods that used that more concise style.

The percentage of 235U versus 238U should be configurable. On earth, they were originally equally abundant, but 235U has a shorter half life. The 0.7% point is just where the earth is now, and as such is an unlikely point for an alien planet unless it is exactly the same age as earth.