Q:

mapping custom data RxAndroid with Kotlin

I am trying to convert examples from this article from Java to Kotlin.
I get error from picture at Exmaple 5:

And I noticed, that without map() function I don't get this error

So, what the point of this error and how to write it right?

A:

The return value of a lambda in Kotlin is always the last expression in the block. 
So in this case the result of
.map { it.note = it.note.toUpperCase() }

is not returning a meaningful value.
What you should do instead is this
.map { 
    it.note = it.note.toUpperCase()
    it
}

Which returns a type of Note instead of Unit.

