fun <T, R : Any> Sequence<T>.mapNotNull(
    transform: (T) -> R?
): Sequence<R>

Returns a sequence containing only the non-null results of applying the given transform function to each element in the original sequence.

The operation is intermediate and stateless.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings: List<String> = listOf("12a", "45", "", "3")
val ints: List<Int> = strings.mapNotNull { it.toIntOrNull() }

println(ints) // [45, 3]
println(ints.sum()) // 48
//sampleEnd
}