Collect to map skipping null values

Actually, a slight change to pwolaq’s answer guarantees that the second item is non-nullable:

val map = listOf(Pair("a", 1), Pair("b", null), Pair("c", 3), Pair("d", null))
    .mapNotNull { p -> p.second?.let { Pair(p.first, it) } }
    .toMap()
println(map)

This will give you a Map<String, Int>, since mapNotNull ignores anything that maps to null, and using let with the safe call operator ?. returns null if its receiver (p.second) is null.

This is basically what you stated in your question, made shorter with let.