Some Sender Options are not applied at Sender Initialization

[karenychen]

go-shuttle/v2/sender.go

Lines 55 to 60 in 9be33d2

	if options == nil {
	options = &SenderOptions{Marshaller: &DefaultJSONMarshaller{}}
	}
	if options.SendTimeout == 0 {
	options.SendTimeout = defaultSendTimeout
	}

If senderOption is not nil, then we never set default Marshaller. The sender will run into a nil pointer dereference and panic.