<Kotlin: Type inference failed. The value of the t...

# stackoverflow

[user]

Kotlin: Type inference failed. The value of the type parameter T should be mentioned in input types
I'm new to Kotlin, for the piece of the below code:
fun a(stcd: String) {
val res = mutableSetOf()
val aaa = mutableListOf()
aaa.stream().filter { x: Map -> x.isNotEmpty() }
.filter { x: Map ->
x.values.contains(stcd) // throws error
}.forEach { x: Map ->
x.forEach { (k: String, v: Set?) ->
res.add(k)
}
}
}

Could anyone point out why contains throws error:Type...