Hey, to follow up on my previous message; it seems that the game will force snap-to-grid for the terraformer, even though it seems that it initially would not (by selecting it in your inventory to place down. It would still be nice to make sure it also snaps to grid during "placing it down".)
Some more analysis for you:
control.lua line line #815:
script.on_event(defines.events.on_sector_scanned, function(event)
Is the event that triggers the error, it moves to line #825 in the same file, which requests for the recipe. This leads to...
control_arboretum.lua line #27:
if recipe ~= nil and ArboretumTable.inventory.fluidbox[1] ~= nil then
Omnifluids attempts to change all recipes to require solid objects instead of fluids (A few exceptions exist). This mod was developed to reduce UPS usage by reducing requirements for pipes (fluids). Your control_arboretum.lua line #27 is probably looking for a fluidbox that doesn't exist because Omnifluid changed the recipes to solids. However, I am not proficient enough with lua to suggest an exact solution to this problem to you.
You could probably change the code to something like "if the recipe requires fluids... elseif..."
Hope my garbling was at least somewhat useful to you. Good luck, absolutely love your mod!