Help me out with what you want `ContentAsText` to look like:  

    public static string ContentAsText(this Blob blob, Encoding encoding = null, FilteringOptions filteringOptions = null)

It looks to me like:

    `ContentAsText();` is a legit call
    `ContentAsText(new FilteringOptions());` is not, one would have to call `ContentAsText(null, new FilteringOptions())`?

Is this expected?