public abstract Task CloseAsync(
	CancellationToken cancellationToken = null
)

Public MustOverride Function CloseAsync ( 
	Optional cancellationToken As CancellationToken = Nothing
) As Task

abstract CloseAsync : 
        ?cancellationToken : CancellationToken 
(* Defaults:
        let _cancellationToken = defaultArg cancellationToken null
*)
-> Task