Optional for android api lower than 24.

Optional.kt

class Optional<T> {

    private var value: T? = null

    private constructor() {
        this.value = null
    }

    private constructor(value: T) {
        this.value = value
    }

    fun ifPresent(action: (T) -> Unit) {
        if (value != null) {
            action(value!!)
        }
    }

    fun ifPresentOrElse(action: (T) -> Unit, orElse: () -> Unit) {
        if (value != null) {
            action(value!!)
        } else orElse()
    }

    fun isPresent() = value != null

    fun get() = value!!

    companion object {

        @JvmStatic
        fun <T> empty(): Optional<T> {
            return Optional()
        }

        @JvmStatic
        fun <T> of(value: T): Optional<T> {
            return Optional(value)
        }
    }

}

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