inline fun <R : Any, C : MutableCollection<in R>> CharSequence.mapIndexedNotNullTo( destination: C, transform: (index: Int, Char) -> R? ): C
Applies the given transform function to each character and its index in the original char sequence and appends only the non-null results to the given destination.
 transform - function that takes the index of a character and the character itself and returns the result of the transform applied to the character.
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Licensed under the Apache License, Version 2.0.
    https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.text/map-indexed-not-null-to.html