Kotlin toMap collector with duplicate keys

I'm looking for Kotlin analogue for Java stream collector Collectors.toMap with mergeFunction parameter.

For instance, in Java in order to count chars in String it's possible to use the following code snippet:

Map<Character, Integer> charsMap = s2.chars()
            .mapToObj(c -> (char) c)
            .collect(Collectors.toMap(Function.identity(), s -> 1, Integer::sum));

If we convert the Java snippet to Kotlin it looks rather ugly because of explicit types usage.

private fun countCharsV2(word: String): Map<Char, Int> {
    return word.chars()
        .mapToObj { it.toChar() }
        .collect(
            Collectors.toMap(
                Function.identity(),
                Function { 1 },
                BinaryOperator { a: Int, b: Int -> Integer.sum(a, b) }
            )
        )
}

Is there a Kotlin collector with similar behaviour?