def myList = [1,2,3,4,5,6,7,8,9,10]
def emptyList = []

def check(List<Integer> list) {
    def counter = 0

    if (list.size() == 0) {
        return "Die übergebene Liste ist leer!"
    }
    for(int i = 0; i < list.size(); i++) {
        if(list[i] % 2 == 0) {
            counter++
        }
    }
    return counter
}

println check(myList)
println check(emptyList)