Attempt to Index "?" a nil value - OpenP

Hello everyone.

I'm working on a project for a build of a rather large build. The project and program is set up to make sure that certain Thermal Expansion RF storage blocks don't drop below a specific value. I figured the hard part of this project was going to be learning how to wrap peripherals, but I'm not sure now I was right.

Code follows. The "Attempt to Index '?' a nil value" error hits at line 16… after allowing the same method to be called several times.

cellScience = peripheral.wrap("cofh_thermalexpansion_energycell_1")
cellIndustry = peripheral.wrap("cofh_thermalexpansion_energycell_2")
cellMENet = peripheral.wrap("cofh_thermalexpansion_energycell_3")
cellAgro = peripheral.wrap("cofh_thermalexpansion_energycell_4")
cellNuke = peripheral.wrap("cofh_thermalexpansion_energycell_5")
monitor = peripheral.wrap("monitor_1")
--The above block wraps all the relevant peripherals

--term.redirect(monitor) -- leashes everything to the monitor/commented out for testing

while true do
  --These variables are in the loop to re-calculate on every pass.
  maxScience = cellScience.getMaxEnergyStored("unknown")
  maxIndustry = cellIndustry.getMaxEnergyStored("unknown")
  maxMENet = cellMENet.getMaxEnergyStored("unknown")
  maxAgro = cellAgro.getMaxEnergyStored("unknown")
  maxNuke = cellNuke.getMaxEnergyStored("unknown")
  capScience = cellScience.getEnergyStored("unknown")
  capIndustry = cellIndustry.getEnergyStored("unknown")
  capMENet = cellMENet.getEnergyStored("unknown")
  capAgro = cellAgro.getEnergyStored("unknown")
  capNuke = cellNuke.getEnergyStored("unknown")

  monitor.clear()
  term.setCursorPos(1, 1)
  print("Testing Substation Charge:")
  sleep(5)

  --if derivations test each set. 5 total taking 5s each.
  if capAgro/maxAgro > 3/4 then
	print("Agricultural Substation Nominal")
  else
	print("Agricultural Substation Discharging")
  end
  sleep(5)

  if capIndustry/maxIndustry > 3/4 then
	print("Industrial Substation Nominal")
  else
	print("Industrial Substation Discharging")
  end
  sleep(5)

  if capMENet/maxMENet > 3/4 then
	print("M/E Network Substation Nominal")
  else
	print("M/E Network Substation Discharging")
  end
  sleep(5)

  if capNuke/maxNuke > 3/4 then
	print("Nuclear Facility Substation Nominal")
  else
	print("Nuclear Facility Substation Discharging")
  end
  sleep(5)

  if capScience/maxScience > 3/4 then
	print("Science Substation Nominal")
  else
	print("Science Substation Discharging")
  end

  print("Testing Complete.")
  sleep(40) -- sum of sleep = 60 seconds
end --closes the loop

Pastebin: http://pastebin.com/Wt6QvEt2

Edit: I am chiefly confused by the several lines of identical code before :16: that work just fine.

Communeguy, on 20 November 2014 - 07:13 PM said:

-snip

Although this might sound obvious… Have you made sure there is a energy cell 4? You should be able to print(type(cellAgro)) and it should return table.

Yeah, I feel stupid now. You're totally right. It was plugged into what I thought was the network for this system, and was actually another network. After relaying the cable, it worked fine on the first attempt.