Converting to Roman Numerals using an array of tuples

RomanTuples.swift

func toRomanNumerals(number: Int) -> String? {
    guard number > 0 else {
        return nil
    }
    
    var remainder = number
    
    let values = [("M", 1000), ("CM", 900), ("D", 500), ("CD", 400), ("C",100), ("XC", 90), ("L",50), ("XL",40), ("X",10), ("IX", 9), ("V",5),("IV",4), ("I",1)]
    
    var result = ""
    
    for (romanChar, arabicValue) in values {
        let count = remainder / arabicValue
        
        if count == 0 { continue }
        
        for _ in 1...count
        {
            result += romanChar
            remainder -= arabicValue
        }
    }
    
    return result
}

toRomanNumerals(2014) // optional, otherwise toRomanTuple(2014)!
toRomanNumerals(-3) // nil

In beta 5 1...count gives an error if the range is invalid (1...0), so now I have to check for that condition

Swift 2.2 quite rightly complains about my var param, and guard is probably better than my if check.