为什么lambda调用有2个堆栈帧？

Question

以下代码：

public static void main(String[] args) {
    Collections.singleton(1).stream().forEach(i -> new Exception().printStackTrace());
}

打印：

java.lang.Exception
    at PrintLambdaStackTrace.lambda$main$0(PrintLambdaStackTrace.java:6)
    at PrintLambdaStackTrace$$Lambda$1/1831932724.accept(Unknown Source)
    at java.util.Collections$2.tryAdvance(Collections.java:4717)
    at java.util.Collections$2.forEachRemaining(Collections.java:4725)
    at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580)
    at PrintLambdaStackTrace.main(PrintLambdaStackTrace.java:6)

如何实现lambda调用？为什么有2个堆栈帧？