I did mention all of this: "[...] but Kotlin still needs to support [platform types] to maintain compatibility with underlying platforms that support unspecifi

I did mention all of this: "[...] but Kotlin still needs to support [platform types] to maintain compatibility with underlying platforms that support unspecified nullability, such as the JVM and JavaScript." To be more accurate, "platform types" are not used with JavaScript, but you do get something similar in that case. I haven't worked with Kotlin/JS at all, but from my understanding if you do not have proper type definitions, you have to deal with dynamic types - which are also nullable.