Attempt to compare nil with number error need help

local y = 0
local x = 0
local fuel = 1
local sappling = 2
local bone = 3

term.clear()
term.setCursorPos(1,1)
print("Should turtle plant too?")
write("Yes = 1 / No = 2): ")
local answer1 = tonumber(io.read())
if answer1 == 1 then
write("Loop: ")
local loop = tonumber(io.read())
term.setCursorPos(1,3)
else
loop = 1
end

print("Lumberjack has started")
m = peripheral.wrap("right")
m.link()
function Resupply()
m.resupply(fuel)
m.resupply(sappling)
m.resupply(bone)
end
function Refuel()
if turtle.getFuelLevel() < 20 then
Resupply()
turtle.select(fuel)
turtle.refuel(1)
end
end

while x < loop do -- the error is here somewhere this is line 47
Resupply()
if answer1 == 1 then
Refuel()
turtle.forward()
turtle.up()
turtle.select(sappling)
turtle.forward()
turtle.placeDown()
turtle.forward()
turtle.placeDown()
turtle.turnRight()
turtle.forward()
turtle.placeDown()
turtle.turnRight()
turtle.forward()
turtle.placeDown()
turtle.turnRight()
turtle.forward()
turtle.placeDown()
turtle.turnLeft()
turtle.forward()
turtle.down()
turtle.turnRight()
turtle.turnRight()
turtle.select(bone)
turtle.place()
turtle.place()
turtle.place()
--turtle.place()
turtle.turnRight()
turtle.turnRight()
turtle.forward()
turtle.turnRight()
turtle.turnRight()
turtle.select(fuel)
turtle.refuel(1)
end
turtle.forward()
turtle.dig()
turtle.forward()
turtle.dig()
turtle.forward()

turtle.turnRight()
turtle.dig()
turtle.forward()
turtle.turnRight()
turtle.dig()
turtle.forward()
turtle.turnRight()
turtle.dig()
turtle.forward()
turtle.turnRight()
print("Tree is ready to get cutted")
print("loop has started")
while turtle.detectUp() do
 
Refuel()
turtle.digUp()
turtle.forward()
turtle.digUp()
turtle.turnRight()
turtle.forward()
turtle.digUp()
turtle.turnRight()
turtle.forward()
turtle.digUp()
turtle.turnRight()
turtle.forward()
turtle.digUp()
turtle.turnRight()
turtle.up()
y = y + 1
end 

Refuel()
while not turtle.detectDown() do
turtle.down()
end
turtle.turnRight()
turtle.turnRight()
turtle.forward()
turtle.forward()
turtle.select(4)
turtle.drop(64)
turtle.select(5)
turtle.drop(64)
turtle.select(6)
turtle.drop(64)
turtle.turnLeft()
turtle.turnLeft()
turtle.select(fuel)
term.clear()
x = x + 1
end
term.setCursorPos(1,  1)
print("Turtle is done")

local loop = 0