in reactor/Core/src/jetbrains/mps/logic/reactor/core/CompositeFeedback.kt [104:110]
fun of(left: Feedback?, right: Feedback?): Feedback? {
return if (left == null || right == null) {
left ?: right
} else (left as? CompositeFeedback)?.composeRight(right)
?: ((right as? CompositeFeedback)?.composeLeft(left) ?: CompositeFeedback(listOf(left, right)))
}