RXJava 范围给了我类型推断失败的错误

RXJava Range gave me error of Type inference failed

在阅读有关 RXJAVA 的书籍时，出现以下错误：

Type inference failed. Expected type mismatch: inferred type is Observable! but Observable was expected

来自这个简单的片段：

@Test
    fun deferable() {
       val source= Observable.range(1, 5)
                source.subscribe { s -> System.out.println("RECEIVED: $s "}
    }

我不明白我为什么在 运行 测试时收到这条奇怪的消息。在我的日常活动中，我管理这种错误更改 variable/property 的 return （表达式类型） 作为 val source :Observable<Int>

但不起作用，我也尝试做一些 map{it.toString()} 但是没有成功，我怎样才能让 "test" 通过呢？我知道这不是真正的测试，我只是用它来学习 RXJAVA，所以没有断言，我希望看到这个输出：

RECEIVED:5
RECEIVED:6
RECEIVED:7
RECEIVED:8
RECEIVED:9
RECEIVED:10
RECEIVED:11
RECEIVED:12
RECEIVED:13
RECEIVED:14

Type inference failed. Expected type mismatch: inferred type is Observable! but Observable was expected

如果您遇到此类编译器错误，则意味着您正在尝试传递可空值而不是非空值。你看到尖叫者：Observable! 标志了吗？事情是这样的。
PS。在我的电脑上测试是绿色的。接下来是输出：

RECEIVED: 1 
RECEIVED: 2 
RECEIVED: 3 
RECEIVED: 4 
RECEIVED: 5