Why doesn't sumBy(selector) return Long? : <p><a href="https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum-by.html" rel="noreferrer">sumBy(selector)</a> returns Int</p>

<p><a href="https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum-by-double.html" rel="noreferrer">sumByDouble(selector)</a> returns Double</p>

<p>Why doesn't sumBy return Long? Is there a workaround for this?</p>
