requireNoNulls

Returns an original collection containing all the non-null elements, throwing an IllegalArgumentException if there are any null elements.

fun <T : Any> Sequence<T?>.requireNoNulls(): Sequence<T>(source)

val nullableInts = listOf(1, null, 3)
val nonNullInts: List<Int> = nullableInts
    .asSequence()
    .requireNoNulls()
    .toList()   // throws IllegalArgumentException because of the null

Source