如何判断source是否为空？

if source is None:
    print("source为空")
else:
    print("source不为空")

if len(source) == 0:
    print("source为空")
else:
    print("source不为空")

if (source.equals("")) {
    System.out.println("source为空");
} else {
    System.out.println("source不为空");
}

if (string.IsNullOrEmpty(source)) {
    Console.WriteLine("source为空");
} else {
    Console.WriteLine("source不为空");
}