Random array string getting nil - ios

Question

I am using the random range function to my array string. Also I am using a filter to not repeat to my array string, but sometimes my first random string is nil.
Random range code:
func randomNumber(range: Range<Int> = 1...6) -> Int {
let min = range.startIndex
let max = range.endIndex
return Int(arc4random_uniform(UInt32(max - min))) + min
}
I'm getting nil from the firstItem:
var a = cities[randomNumber(0...80)]
if Marmara.contains(a){
firstItem = a
print(firstItem) //It's getting nil sometimes.
var filteredForSecond = Marmara.filter{$0 != firstItem}
secondItem = filteredForSecond[randomNumber(0...filteredForSecond.count-1)]
print(secondItem)
var filteredForThird = Marmara.filter{$0 != secondItem && $0 != firstItem}
thirdItem = filteredForThird[randomNumber(0...filteredForThird.count-1)]
print(thirdItem)
var filteredForFourth = Marmara.filter{$0 != thirdItem && $0 != secondItem && $0 != firstItem}
print(fourthItem)
fourthItem = filteredForFourth[randomNumber(0...filteredForFourth.count-1)]
//sehirler.removeAtIndex(s)
print("\(firstItem), \(secondItem), \(thirdItem), \(fourthItem)")
}
I have an "81" string in the array using this code. What should I do to fix this nil string problem?

Answer 1

I would at least make the following change. See if this fixes the problem.
var a = cities[randomNumber(0...cities.count-1)]

Answer 2

I solved the problem. I'm checking if it is nil, taking again random string and it's not getting nil anymore.
Here is the working code:
var a = cities[randomNumber(0...cities.count-1)]
while a.isEmpty{
a = cities[randomNumber(0...cities.count-1)]
}
if Marmara.contains(a) && a != ""{
firstItem = a
if firstItem.isEmpty{
print("nil")
}
print(firstItem)
var filteredForSecond = Marmara.filter{$0 != firstItem}
secondItem = filteredForSecond[randomNumber(0...filteredForSecond.count-1)]
print(secondItem)
var filteredForThird = Marmara.filter{$0 != secondItem && $0 != firstItem}
thirdItem = filteredForThird[randomNumber(0...filteredForThird.count-1)]
print(thirdItem)
var filteredForFourth = Marmara.filter{$0 != thirdItem && $0 != secondItem && $0 != firstItem}
print(fourthItem)
fourthItem = filteredForFourth[randomNumber(0...filteredForFourth.count-1)]
//sehirler.removeAtIndex(s)
print("\(firstItem), \(secondItem), \(thirdItem), \(fourthItem)")
}