null safety with conditional if

KotlinBasics.kt

// check for null in conditions
val trainingName: String? = "Learn Kotlin in 45 minutes"
if (trainingName != null && trainingName.isNotEmpty()) {
    print("String of length ${trainingName.length}")
} else {
    print("Empty string")
}

val platform: String? = null
val language = "Kotlin"

println(platform?.length) // safe call
println(language.length) // unnecessary safe call

val lengthOfWord = platform!!.length // !! operator

val numberOfLetters: Int? = lengthOfWord as? Int // safe cast