suspending
fun <E> <Error class: unknown class><E>.suspendingHandler(server: <Error class: unknown class>, listener: suspend (E) -> Unit): <Error class: unknown class><E>
fun <E> <Error class: unknown class><E>.suspendingHandler(extension: <Error class: unknown class>, listener: suspend (E) -> Unit): <Error class: unknown class><E>
Adds a new suspendable handler to this builder.