A platform type arises when Kotlin calls a Java method with no nullability annotation, e.g. `val s = javaList.get(0)` where the element type is denoted `String!`. Which statement about how platform types are represented and checked is correct?
// javaList is a Java List<String> with no @Nullable/@NotNull
val s = javaList.get(0) // type is String!
val len = s.length // treated as non-null here