［Swift中错误］missing argument label 'greeting:' in call

Swift 中出现这个问题：从第二个参数起，自动加上lable

func sayHello(name:String? ,greeting:String)->String
{
    let result = greeting + "," + (name ?? "Guest") + "!"
    return result
}

var nickname:String?
nickname = "yc"
//“Goodmorning前面应该增加greeting：”
print( sayHello("yc","Goodmoring") )

［Swift中错误］missing argument label 'greeting:' in call