Undefined method '[]' I dont know why

Hello , I have problem with my script.

/////////////this function return true or false
def moznazbudowac?(co,sesja,stan)
budynek = “”
catch(:redo) do
case co
when 1
budynek = “Kopalnia metalu”
when 2
budynek = “Kopalnia krysztalu”
when 3
budynek = “Kopalnia deuteru”
end
end
poziom = stan[budynek] # 11
poziom = poziom.to_i
surowce_pods = bazadanych(co) #output
[60,15,0,1.5]
surowce_potrz = [0,0,0,0]
surowce_potrz[0] = surowce_pods[0].to_i
surowce_pods[3].to_i*(poziom-1)#Error
[…]# further part of script
//////////////////////

Error : Undefined method ‘[]’ for nil:NilClass
I try to modify script but dont know how fix this error.

a = moznazbudowac?(1,sesja,stan) // this is working

But when i execute this
sesja = sesja()
stan = skaner ()
kolejka() return array i was testing with array [1]
test_kolejki = kolejka()
kolejkowanie(test_kolejki,sesja,stan)#error
I have error in function kolejkowanie() and i line above and in function
moznazbudowac?.

/////////////////
def kolejkowanie(kolejka,sesja,stan)
dlugosc = kolejka.length
dlugosc -=1
nr = 0
while nr<=dlugosc
zbudowano = 0
while zbudowano == 0
if moznazbudowac?(kolejka[nr],sesja,stan) == true then#error
zbuduj(kolejka[nr],sesja)
kolejka.pop
nr +=1
zbudowano = 1
else
“Nie starczy surowcow”
end
end

end

end
///////////////////

Hi,
Well, it’s really telling you that something that you’re indexing into
is nil. Not sure which of the things in that big assignment is the nil
one, but something there is.

HTH,
Carey

Thx for help. Now i see what’s wrong:
if moznazbudowac?(kolejka[nr],sesja,stan) == true

kolejka does error. I will fix this tomorrow.