Kotlin user with nulls

KotlinUserWithNulls.kt

data class KotlinUserWithNulls(val firstName: String?,
       // String? means that it is either a String object or a null
                               val lastName: String?,
                               val addresses: List<Address> =  listOf()) {

    data class Address(val city: String?)

    companion object {
        fun fetchFirstCity(user: KotlinUserWithNulls?): String? {
            user?.addresses?.forEach { it.city?.let { return it } }
            return null
        }
    }
}