Merge a list of maps

Hello, I’m trying to understand some Kotlin data mapping functions (which are a lot of them and there is a need to read a separate book). The case is next: I need to flat List<HashMap<String, List<String>>> and merge all the values. So, I found a solution:

    fun foldMap() {
        val list = listOf(
            hashMapOf("A" to listOf("a1", "a2"), "B" to listOf("b1", "b2")),
            hashMapOf("A" to listOf("a11", "a21"), "C" to listOf("c11", "c21")),
            hashMapOf("C" to listOf("c12", "c22"))

        val map = list.fold(hashMapOf<String, List<String>>()) { acc, curr ->
            curr.forEach { entry ->
                acc.merge(entry.key, entry.value) { new, old -> new + old }

        assertEquals("{A=[a1, a2, a11, a21], B=[b1, b2], C=[c11, c21, c12, c22]}", map.toString())

Can the map calculation be shorter?