Spot the error

This Swift code contains one error – can you select the line that is incorrect?

Tip: You should mentally run the code from top to bottom, meaning that if line 3 says an integer should be returned and line 10 tries to return a string, line 10 is the wrong one.

func convertValue(score: Int) -> String {

    var str: String = "The score is "

    str += String(score)

    return str

}

print(convertValue(score; 38))