public static Task<Nullable<double>> AverageAsync<TSource>(
	this IMongoQueryable<TSource> source,
	Expression<Func<TSource, Nullable<long>>> selector,
	CancellationToken cancellationToken = null
)

<ExtensionAttribute>
Public Shared Function AverageAsync(Of TSource) ( 
	source As IMongoQueryable(Of TSource),
	selector As Expression(Of Func(Of TSource, Nullable(Of Long))),
	Optional cancellationToken As CancellationToken = Nothing
) As Task(Of Nullable(Of Double))

[<ExtensionAttribute>]
static member AverageAsync : 
        source : IMongoQueryable<'TSource> * 
        selector : Expression<Func<'TSource, Nullable<int64>>> * 
        ?cancellationToken : CancellationToken 
(* Defaults:
        let _cancellationToken = defaultArg cancellationToken null
*)
-> Task<Nullable<float>>