Solutions should not promote usage of `!!`

[alban-auzeill]

For example in Properties/Lazy property/src/Task.kt the solution:

class LazyProperty(val initializer: () -> Int) {
    var value: Int? = null
    val lazy: Int
        get() {
            if (value == null) {
                value = initializer()
            }
            return value!!
        }
}

Would be safer using:

class LazyProperty(val initializer: () -> Int) {
    private var value: Int? = null
    val lazy: Int
        get() = value ?: initializer().also { value = it }
}