A SinkTIn, TMat that materializes into a TaskTResult of the first value received. If the stream completes before signaling at least a single element, the Task will return default value. If the stream signals an error errors before signaling at least a single element, the Task will be failed with the streams exception.

public static Sink<TIn, Task<TIn>> FirstOrDefault<TIn>()

static member FirstOrDefault : unit -> Sink<'TIn, Task<'TIn>>